How to Integrate ILMerge into Visual Studio Build Process to Merge Assemblies?

Here an alternative solution:

1) Install ILMerge.MSBuild.Tasks package from nuget

PM> Install-Package ILMerge.MSBuild.Tasks

2) Edit the *.csproj file of the project that you want to merge by adding the code below:

  <!-- Code to merge the assemblies into one:setup.exe -->
  <UsingTask TaskName="ILMerge.MSBuild.Tasks.ILMerge" AssemblyFile="$(SolutionDir)\packages\ILMerge.MSBuild.Tasks.1.0.0.3\tools\ILMerge.MSBuild.Tasks.dll" />
  <Target Name="AfterBuild">
    <ItemGroup>
      <MergeAsm Include="$(OutputPath)$(TargetFileName)" />
      <MergeAsm Include="$(OutputPath)LIB1_To_MERGE.dll" />
      <MergeAsm Include="$(OutputPath)LIB2_To_MERGE.dll" />
    </ItemGroup>
    <PropertyGroup>
      <MergedAssembly>$(ProjectDir)$(OutDir)MERGED_ASSEMBLY_NAME.exe</MergedAssembly>
    </PropertyGroup>
    <Message Text="ILMerge @(MergeAsm) -&gt; $(MergedAssembly)" Importance="high" />
    <ILMerge InputAssemblies="@(MergeAsm)" OutputFile="$(MergedAssembly)" TargetKind="SameAsPrimaryAssembly" />
  </Target>

3) Build your project as usual.

The "MSBuild ILMerge task" (or MSBuild.ILMerge.Task) NuGet package makes this process quite simple. It defaults to merging any "copy local" references into your main assembly.

Note: Although the packages have similar names, this one is different from ILMerge.MSBuild.Tasks that Davide Icardi mentioned in his answer. The one I'm suggesting here was first published in August 2014.