diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,11 @@
 # Changelog for persistent
 
+## 2.14.2.0
+
+* [#1421](https://github.com/yesodweb/persistent/pull/1421)
+    * Add `mpsCamelCaseCompositeKeySelector` field to `MkPersistSettings`,
+      which define the style of the entity's composite key.
+      
 ## 2.14.1.0
 
 * [#1418](https://github.com/yesodweb/persistent/pull/1418/)
diff --git a/Database/Persist/TH.hs b/Database/Persist/TH.hs
--- a/Database/Persist/TH.hs
+++ b/Database/Persist/TH.hs
@@ -39,6 +39,7 @@
     , mpsEntityJSON
     , mpsGenerateLenses
     , mpsDeriveInstances
+    , mpsCamelCaseCompositeKeySelector
     , EntityJSON(..)
     , mkPersistSettings
     , sqlSettings
@@ -991,6 +992,33 @@
     -- ^ TODO: document
     --
     -- @since 2.13.0.0
+    , mpsCamelCaseCompositeKeySelector :: Bool
+    -- ^ Should we generate composite key accessors in the correct CamelCase style.
+    --
+    -- If the 'mpsCamelCaseCompositeKeySelector' value is set to 'False',
+    -- then the field part of the accessor starts with the lowercase.
+    -- This is a legacy style.
+    --
+    -- @
+    -- data Key CompanyUser = CompanyUserKey
+    --   { companyUserKeycompanyId :: CompanyId
+    --   , companyUserKeyuserId :: UserId
+    --   }
+    -- @
+    --
+    -- If the 'mpsCamelCaseCompositeKeySelector' value is set to 'True',
+    -- then field accessors are generated in CamelCase style.
+    --
+    -- @
+    -- data Key CompanyUser = CompanyUserKey
+    --   { companyUserKeyCompanyId :: CompanyId
+    --   , companyUserKeyUserId :: UserId
+    --   }
+    -- @
+
+    -- Default: False
+    --
+    -- @since 2.14.2.0
     }
 
 {-# DEPRECATED mpsGeneric "The mpsGeneric function adds a considerable amount of overhead and complexity to the library without bringing significant benefit. We would like to remove it. If you require this feature, please comment on the linked GitHub issue, and we'll either keep it around, or we can figure out a nicer way to solve your problem.\n\n Github: https://github.com/yesodweb/persistent/issues/1204" #-}
@@ -1035,6 +1063,7 @@
     , mpsDeriveInstances = []
     , mpsImplicitIdDef =
         autoIncrementingInteger
+    , mpsCamelCaseCompositeKeySelector = False
     }
 
 -- | Use the 'SqlPersist' backend.
@@ -3088,7 +3117,11 @@
     | pkNewtype mps entDef =
         unKeyName entDef
     | otherwise =
-        mkName $ T.unpack $ lowerFirst (keyText entDef) `mappend` unFieldNameHS fieldDef
+        mkName $ T.unpack $ lowerFirst (keyText entDef) `mappend` fieldName
+    where
+      fieldName = modifyFieldName (unFieldNameHS fieldDef)
+      modifyFieldName =
+        if mpsCamelCaseCompositeKeySelector mps then upperFirst else id
 
 filterConName
     :: MkPersistSettings
diff --git a/persistent.cabal b/persistent.cabal
--- a/persistent.cabal
+++ b/persistent.cabal
@@ -1,5 +1,5 @@
 name:            persistent
-version:         2.14.1.0
+version:         2.14.2.0
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -166,6 +166,7 @@
         Database.Persist.PersistValueSpec
         Database.Persist.QuasiSpec
         Database.Persist.TH.CommentSpec
+        Database.Persist.TH.CompositeKeyStyleSpec
         Database.Persist.TH.DiscoverEntitiesSpec
         Database.Persist.TH.EmbedSpec
         Database.Persist.TH.ForeignRefSpec
diff --git a/test/Database/Persist/TH/CompositeKeyStyleSpec.hs b/test/Database/Persist/TH/CompositeKeyStyleSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/Database/Persist/TH/CompositeKeyStyleSpec.hs
@@ -0,0 +1,62 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module Database.Persist.TH.CompositeKeyStyleSpec where
+
+import Data.Data (Data, constrFields, toConstr)
+import Data.Text (Text)
+import Database.Persist.Sql
+import Database.Persist.TH
+import Test.Hspec hiding (Selector)
+
+mkPersist sqlSettings
+  [persistLowerCase|
+    CompanyUserLegacyStyle
+      companyName Text
+      userName Text
+      Primary companyName userName
+  |]
+
+deriving instance Data CompanyUserLegacyStyle
+deriving instance Data (Key CompanyUserLegacyStyle)
+
+mkPersist sqlSettings {mpsCamelCaseCompositeKeySelector = True}
+  [persistLowerCase|
+    CompanyUserCamelStyle
+      companyName Text
+      userName Text
+      Primary companyName userName
+  |]
+
+deriving instance Data CompanyUserCamelStyle
+deriving instance Data (Key CompanyUserCamelStyle)
+
+spec :: Spec
+spec = describe "CompositeKeyStyleSpec" $ do
+  describe "mpsCamelCaseCompositeKeySelector is False" $ do
+    it "Should generate Legacy style key selectors" $ do
+      let key = CompanyUserLegacyStyleKey "cName" "uName"
+
+      constrFields (toConstr key)
+        `shouldBe`
+          [ "companyUserLegacyStyleKeycompanyName"
+          , "companyUserLegacyStyleKeyuserName"
+          ]
+  describe "mpsCamelCaseCompositeKeySelector is True" $ do
+    it "Should generate CamelCase style key selectors" $ do
+      let key = CompanyUserCamelStyleKey "cName" "uName"
+
+      constrFields (toConstr key)
+        `shouldBe`
+          [ "companyUserCamelStyleKeyCompanyName"
+          , "companyUserCamelStyleKeyUserName"
+          ]
diff --git a/test/Database/Persist/THSpec.hs b/test/Database/Persist/THSpec.hs
--- a/test/Database/Persist/THSpec.hs
+++ b/test/Database/Persist/THSpec.hs
@@ -1,10 +1,10 @@
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DerivingStrategies #-}
 {-# LANGUAGE ExistentialQuantification #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes #-}
@@ -24,8 +24,6 @@
 
 module Database.Persist.THSpec where
 
-import System.Environment
-import Data.Time
 import Control.Applicative (Const(..))
 import Data.Aeson (decode, encode)
 import Data.ByteString.Lazy.Char8 ()
@@ -35,7 +33,9 @@
 import qualified Data.List as List
 import Data.Proxy
 import Data.Text (Text, pack)
+import Data.Time
 import GHC.Generics (Generic)
+import System.Environment
 import Test.Hspec
 import Test.Hspec.QuickCheck
 import Test.QuickCheck.Arbitrary
@@ -50,25 +50,26 @@
 
 
 import qualified Database.Persist.TH.CommentSpec as CommentSpec
+import qualified Database.Persist.TH.CompositeKeyStyleSpec as CompositeKeyStyleSpec
 import qualified Database.Persist.TH.DiscoverEntitiesSpec as DiscoverEntitiesSpec
 import qualified Database.Persist.TH.EmbedSpec as EmbedSpec
 import qualified Database.Persist.TH.ForeignRefSpec as ForeignRefSpec
 import qualified Database.Persist.TH.ImplicitIdColSpec as ImplicitIdColSpec
 import qualified Database.Persist.TH.JsonEncodingSpec as JsonEncodingSpec
 import qualified Database.Persist.TH.KindEntitiesSpec as KindEntitiesSpec
-import qualified Database.Persist.TH.NestedSymbolsInTypeSpec as NestedSymbolsInTypeSpec
 import qualified Database.Persist.TH.MaybeFieldDefsSpec as MaybeFieldDefsSpec
 import qualified Database.Persist.TH.MigrationOnlySpec as MigrationOnlySpec
 import qualified Database.Persist.TH.MultiBlockSpec as MultiBlockSpec
+import qualified Database.Persist.TH.NestedSymbolsInTypeSpec as NestedSymbolsInTypeSpec
 import qualified Database.Persist.TH.NoFieldSelectorsSpec as NoFieldSelectorsSpec
 import qualified Database.Persist.TH.OverloadedLabelSpec as OverloadedLabelSpec
 import qualified Database.Persist.TH.PersistWithSpec as PersistWithSpec
 import qualified Database.Persist.TH.RequireOnlyPersistImportSpec as RequireOnlyPersistImportSpec
 import qualified Database.Persist.TH.SharedPrimaryKeyImportedSpec as SharedPrimaryKeyImportedSpec
 import qualified Database.Persist.TH.SharedPrimaryKeySpec as SharedPrimaryKeySpec
+import qualified Database.Persist.TH.SumSpec as SumSpec
 import qualified Database.Persist.TH.ToFromPersistValuesSpec as ToFromPersistValuesSpec
 import qualified Database.Persist.TH.TypeLitFieldDefsSpec as TypeLitFieldDefsSpec
-import qualified Database.Persist.TH.SumSpec as SumSpec
 
 -- test to ensure we can have types ending in Id that don't trash the TH
 -- machinery
@@ -198,6 +199,7 @@
     ToFromPersistValuesSpec.spec
     JsonEncodingSpec.spec
     CommentSpec.spec
+    CompositeKeyStyleSpec.spec
     describe "TestDefaultKeyCol" $ do
         let EntityIdField FieldDef{..} =
                 entityId (entityDef (Proxy @TestDefaultKeyCol))