diff --git a/composer.json b/composer.json
index 19de5c3d66a..2eee7c46682 100644
--- a/composer.json
+++ b/composer.json
@@ -61,6 +61,7 @@
             "Rector\\Sensio\\": "packages/Sensio/src",
             "Rector\\Sylius\\": "packages/Sylius/src",
             "Rector\\PHPStan\\": "packages/PHPStan/src",
+            "Rector\\PSR4\\": "packages/PSR4/src",
             "Rector\\PHPUnit\\": "packages/PHPUnit/src",
             "Rector\\Twig\\": "packages/Twig/src",
             "Rector\\TypeDeclaration\\": "packages/TypeDeclaration/src",
diff --git a/config/set/psr-4/psr-4.yaml b/config/set/psr-4/psr-4.yaml
new file mode 100644
index 00000000000..ed67acdc239
--- /dev/null
+++ b/config/set/psr-4/psr-4.yaml
@@ -0,0 +1,2 @@
+services:
+    Rector\PSR4\Rector\Namespace_\NormalizeNamespaceByPSR4ComposerAutoloadRector: ~
diff --git a/docs/AllRectorsOverview.md b/docs/AllRectorsOverview.md
index c8d818a2706..fee242759a7 100644
--- a/docs/AllRectorsOverview.md
+++ b/docs/AllRectorsOverview.md
@@ -1,4 +1,4 @@
-# All 333 Rectors Overview
+# All 334 Rectors Overview
 
 - [Projects](#projects)
 - [General](#general)
@@ -24,6 +24,7 @@
 - [PHPStan](#phpstan)
 - [PHPUnit](#phpunit)
 - [PHPUnitSymfony](#phpunitsymfony)
+- [PSR4](#psr4)
 - [Php](#php)
 - [PhpParser](#phpparser)
 - [PhpSpecToPHPUnit](#phpspectophpunit)
@@ -3236,6 +3237,16 @@ Add response content to response code assert, so it is easier to debug
 
 <br>
 
+## PSR4
+
+### `NormalizeNamespaceByPSR4ComposerAutoloadRector`
+
+- class: `Rector\PSR4\Rector\Namespace_\NormalizeNamespaceByPSR4ComposerAutoloadRector`
+
+Changes namespace and class names to match PSR-4 in composer.json autoload section
+
+<br>
+
 ## Php
 
 ### `AddDefaultValueForUndefinedVariableRector`
diff --git a/packages/PSR4/config/config.yaml b/packages/PSR4/config/config.yaml
new file mode 100644
index 00000000000..5d876ff7ae2
--- /dev/null
+++ b/packages/PSR4/config/config.yaml
@@ -0,0 +1,8 @@
+services:
+    _defaults:
+        public: true
+        autowire: true
+
+    Rector\PSR4\:
+        resource: '../src'
+        exclude: '../src/{Rector/**/*Rector.php}'
diff --git a/packages/PSR4/src/Collector/RenamedClassesCollector.php b/packages/PSR4/src/Collector/RenamedClassesCollector.php
new file mode 100644
index 00000000000..604af245151
--- /dev/null
+++ b/packages/PSR4/src/Collector/RenamedClassesCollector.php
@@ -0,0 +1,24 @@
+<?php declare(strict_types=1);
+
+namespace Rector\PSR4\Collector;
+
+final class RenamedClassesCollector
+{
+    /**
+     * @var string[]
+     */
+    private $renamedClasses = [];
+
+    public function addClassRename(string $oldClass, string $newClass): void
+    {
+        $this->renamedClasses[$oldClass] = $newClass;
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getRenamedClasses(): array
+    {
+        return $this->renamedClasses;
+    }
+}
diff --git a/packages/PSR4/src/Composer/PSR4AutoloadPathsProvider.php b/packages/PSR4/src/Composer/PSR4AutoloadPathsProvider.php
new file mode 100644
index 00000000000..a733d8ffaab
--- /dev/null
+++ b/packages/PSR4/src/Composer/PSR4AutoloadPathsProvider.php
@@ -0,0 +1,61 @@
+<?php declare(strict_types=1);
+
+namespace Rector\PSR4\Composer;
+
+use Nette\Utils\FileSystem;
+use Nette\Utils\Json;
+
+final class PSR4AutoloadPathsProvider
+{
+    /**
+     * @var string[]
+     */
+    private $cachedComposerJsonPSR4AutoloadPaths = [];
+
+    /**
+     * @return string[]
+     */
+    public function provide(): array
+    {
+        if ($this->cachedComposerJsonPSR4AutoloadPaths !== []) {
+            return $this->cachedComposerJsonPSR4AutoloadPaths;
+        }
+
+        $composerJson = $this->readFileToJsonArray($this->getComposerJsonPath());
+        $psr4Autoloads = array_merge(
+            $composerJson['autoload']['psr-4'] ?? [],
+            $composerJson['autoload-dev']['psr-4'] ?? []
+        );
+
+        $this->cachedComposerJsonPSR4AutoloadPaths = $this->removeEmptyNamespaces($psr4Autoloads);
+
+        return $this->cachedComposerJsonPSR4AutoloadPaths;
+    }
+
+    private function getComposerJsonPath(): string
+    {
+        // assume the project has "composer.json" in root directory
+        return getcwd() . '/composer.json';
+    }
+
+    /**
+     * @return mixed[]
+     */
+    private function readFileToJsonArray(string $composerJson): array
+    {
+        $composerJsonContent = FileSystem::read($composerJson);
+
+        return Json::decode($composerJsonContent, Json::FORCE_ARRAY);
+    }
+
+    /**
+     * @param string[] $psr4Autoloads
+     * @return string[]
+     */
+    private function removeEmptyNamespaces(array $psr4Autoloads): array
+    {
+        return array_filter($psr4Autoloads, function ($value): bool {
+            return $value !== '';
+        }, ARRAY_FILTER_USE_KEY);
+    }
+}
diff --git a/packages/PSR4/src/Extension/RenamedClassesReportExtension.php b/packages/PSR4/src/Extension/RenamedClassesReportExtension.php
new file mode 100644
index 00000000000..7d82ba34669
--- /dev/null
+++ b/packages/PSR4/src/Extension/RenamedClassesReportExtension.php
@@ -0,0 +1,116 @@
+<?php declare(strict_types=1);
+
+namespace Rector\PSR4\Extension;
+
+use Nette\Utils\FileSystem;
+use Nette\Utils\Strings;
+use PhpParser\Node\Arg;
+use PhpParser\Node\Expr\FuncCall;
+use PhpParser\Node\Name;
+use PhpParser\Node\Scalar\String_;
+use PhpParser\Node\Stmt\Expression;
+use Rector\Contract\Extension\ReportingExtensionInterface;
+use Rector\PhpParser\Printer\BetterStandardPrinter;
+use Rector\PSR4\Collector\RenamedClassesCollector;
+use Rector\Rector\Class_\RenameClassRector;
+use Symfony\Component\Console\Style\SymfonyStyle;
+use Symfony\Component\Yaml\Yaml;
+
+final class RenamedClassesReportExtension implements ReportingExtensionInterface
+{
+    /**
+     * @var RenamedClassesCollector
+     */
+    private $renamedClassesCollector;
+
+    /**
+     * @var SymfonyStyle
+     */
+    private $symfonyStyle;
+
+    /**
+     * @var BetterStandardPrinter
+     */
+    private $betterStandardPrinter;
+
+    public function __construct(
+        RenamedClassesCollector $renamedClassesCollector,
+        SymfonyStyle $symfonyStyle,
+        BetterStandardPrinter $betterStandardPrinter
+    ) {
+        $this->renamedClassesCollector = $renamedClassesCollector;
+        $this->symfonyStyle = $symfonyStyle;
+        $this->betterStandardPrinter = $betterStandardPrinter;
+    }
+
+    public function run(): void
+    {
+        if ($this->renamedClassesCollector->getRenamedClasses() === []) {
+            return;
+        }
+
+        $data = [
+            # rector.yaml
+            'services' => [
+                RenameClassRector::class => [
+                    '$oldToNewClasses' => $this->renamedClassesCollector->getRenamedClasses(),
+                ],
+            ],
+        ];
+
+        // 1.
+        $yaml = Yaml::dump($data, 5);
+        FileSystem::write(getcwd() . '/rename-classes-rector.yaml', $yaml);
+
+        $nodes = [];
+
+        $renamedClasses = $this->sortInterfaceFirst($this->renamedClassesCollector->getRenamedClasses());
+        foreach ($renamedClasses as $oldClass => $newClass) {
+            $classAlias = new FuncCall(new Name('class_alias'));
+            $classAlias->args[] = new Arg(new String_($newClass));
+            $classAlias->args[] = new Arg(new String_($oldClass));
+
+            $nodes[] = new Expression($classAlias);
+        }
+
+        // 2.
+        $aliasesContent = '<?php' . PHP_EOL . PHP_EOL . $this->betterStandardPrinter->print($nodes);
+        FileSystem::write(getcwd() . '/rename-classes-aliases.php', $aliasesContent);
+
+        // @todo shell exec!?
+        $this->symfonyStyle->warning(
+            'Run: "vendor/bin/rector process tests --config rename-classes-rector.yaml --autoload-file rename-classes-aliases.php" to finish the process'
+        );
+    }
+
+    /**
+     * Interfaces needs to be aliased first, as aliased class needs to have an aliased interface that implements.
+     * PHP will crash with not very helpful "missing interface" error otherwise.
+     *
+     * Also abstract classes and traits, as other code depens on them.
+     *
+     * @param string[] $types
+     * @return string[]
+     */
+    private function sortInterfaceFirst(array $types): array
+    {
+        $interfaces = [];
+        $abstractClasses = [];
+        $traits = [];
+        $classes = [];
+
+        foreach ($types as $oldType => $newType) {
+            if (Strings::endsWith($oldType, 'Interface')) {
+                $interfaces[$oldType] = $newType;
+            } elseif (Strings::contains($oldType, 'Abstract')) {
+                $abstractClasses[$oldType] = $newType;
+            } elseif (Strings::contains($oldType, 'Trait')) {
+                $traits[$oldType] = $newType;
+            } else {
+                $classes[$oldType] = $newType;
+            }
+        }
+
+        return array_merge($interfaces, $traits, $abstractClasses, $classes);
+    }
+}
diff --git a/packages/PSR4/src/Rector/Namespace_/NormalizeNamespaceByPSR4ComposerAutoloadRector.php b/packages/PSR4/src/Rector/Namespace_/NormalizeNamespaceByPSR4ComposerAutoloadRector.php
new file mode 100644
index 00000000000..b335bc92c7f
--- /dev/null
+++ b/packages/PSR4/src/Rector/Namespace_/NormalizeNamespaceByPSR4ComposerAutoloadRector.php
@@ -0,0 +1,153 @@
+<?php declare(strict_types=1);
+
+namespace Rector\PSR4\Rector\Namespace_;
+
+use Nette\Utils\Strings;
+use PhpParser\Node;
+use PhpParser\Node\Name;
+use PhpParser\Node\Stmt\Namespace_;
+use PhpParser\Node\Stmt\Use_;
+use PhpParser\Node\Stmt\UseUse;
+use Rector\NodeTypeResolver\Node\AttributeKey;
+use Rector\PSR4\Collector\RenamedClassesCollector;
+use Rector\PSR4\Composer\PSR4AutoloadPathsProvider;
+use Rector\Rector\AbstractRector;
+use Rector\RectorDefinition\RectorDefinition;
+use Symplify\PackageBuilder\FileSystem\SmartFileInfo;
+
+/**
+ * @sponsor Thanks https://spaceflow.io/ for sponsoring this rule - visit them on https://github.com/SpaceFlow-app
+ */
+final class NormalizeNamespaceByPSR4ComposerAutoloadRector extends AbstractRector
+{
+    /**
+     * @var PSR4AutoloadPathsProvider
+     */
+    private $psR4AutoloadPathsProvider;
+
+    /**
+     * @var RenamedClassesCollector
+     */
+    private $renamedClassesCollector;
+
+    public function __construct(
+        PSR4AutoloadPathsProvider $psR4AutoloadPathsProvider,
+        RenamedClassesCollector $renamedClassesCollector
+    ) {
+        $this->psR4AutoloadPathsProvider = $psR4AutoloadPathsProvider;
+        $this->renamedClassesCollector = $renamedClassesCollector;
+    }
+
+    public function getDefinition(): RectorDefinition
+    {
+        return new RectorDefinition(
+            'Changes namespace and class names to match PSR-4 in composer.json autoload section'
+        );
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getNodeTypes(): array
+    {
+        return [Namespace_::class];
+    }
+
+    /**
+     * @param Namespace_ $node
+     */
+    public function refactor(Node $node): ?Node
+    {
+        $expectedNamespace = $this->getExpectedNamespace($node);
+        if ($expectedNamespace === null) {
+            return null;
+        }
+
+        $currentNamespace = $this->getName($node);
+
+        // namespace is correct → skip
+        if ($currentNamespace === $expectedNamespace) {
+            return null;
+        }
+
+        // change it
+        $node->name = new Name($expectedNamespace);
+
+        // add use import for classes from the same namespace
+        $newUseImports = [];
+        $this->traverseNodesWithCallable($node, function (Node $node) use ($currentNamespace, &$newUseImports) {
+            if (! $node instanceof Name) {
+                return null;
+            }
+
+            /** @var Name|null $originalName */
+            $originalName = $node->getAttribute('originalName');
+            if ($originalName instanceof Name) {
+                if ($currentNamespace . '\\' . $originalName->toString() === $this->getName($node)) {
+                    // this needs to be imported
+                    $newUseImports[] = $this->getName($node);
+                }
+            }
+        });
+
+        $newUseImports = array_unique($newUseImports);
+
+        if ($newUseImports) {
+            $useImports = $this->createUses($newUseImports);
+            $node->stmts = array_merge($useImports, $node->stmts);
+        }
+
+        /** @var SmartFileInfo $smartFileInfo */
+        $smartFileInfo = $node->getAttribute(AttributeKey::FILE_INFO);
+        $oldClassName = $currentNamespace . '\\' . $smartFileInfo->getBasenameWithoutSuffix();
+        $newClassName = $expectedNamespace . '\\' . $smartFileInfo->getBasenameWithoutSuffix();
+
+        $this->renamedClassesCollector->addClassRename($oldClassName, $newClassName);
+
+        // collect changed class
+        return $node;
+    }
+
+    private function getExpectedNamespace(Node $node): ?string
+    {
+        /** @var SmartFileInfo $smartFileInfo */
+        $smartFileInfo = $node->getAttribute(AttributeKey::FILE_INFO);
+
+        $psr4Autoloads = $this->psR4AutoloadPathsProvider->provide();
+
+        foreach ($psr4Autoloads as $namespace => $path) {
+            if (Strings::startsWith($smartFileInfo->getRelativeDirectoryPath(), $path)) {
+                return $namespace . $this->resolveExtraNamespace($smartFileInfo, $path);
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Get the extra path that is not included in root PSR-4 namespace
+     */
+    private function resolveExtraNamespace(SmartFileInfo $smartFileInfo, string $path): string
+    {
+        $extraNamespace = Strings::substring($smartFileInfo->getRelativeDirectoryPath(), Strings::length($path) + 1);
+        $extraNamespace = Strings::replace($extraNamespace, '#/#', '\\');
+
+        return trim($extraNamespace);
+    }
+
+    /**
+     * @param string[] $newUseImports
+     * @return Use_[]
+     */
+    private function createUses(array $newUseImports): array
+    {
+        $uses = [];
+
+        foreach ($newUseImports as $newUseImport) {
+            $useUse = new UseUse(new Name($newUseImport));
+            $uses[] = new Use_([$useUse]);
+        }
+
+        return $uses;
+    }
+}