Web API Activator

UnityApiControllerActivator.cs

public class UnityApiControllerActivator : IHttpControllerActivator
    {
        private readonly IUnityContainer _container;

        public UnityApiControllerActivator(IUnityContainer container)
        {
            _container = container;
        }

        public IHttpController Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)
        {
            return (IHttpController) _container.Resolve(controllerType);
        }
    }

UnityConfig.cs

var container = new UnityContainer();

GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
container.RegisterInstance<IHttpControllerActivator>(new UnityApiControllerActivator(container));