How can I wait till the Parallel.ForEach completes

You don't need that with Parallel.Foreach: it only executes the foreach in as many thread as there are processors available, but it returns synchronously.

More information can be found here

As everyone here said - you dont need to wait for it. What I can add from my experience: If you have an async body to execute and you await some async calls inside, it just ran through my code and did not wait for anything. So I just replaced the await with .Result - then it worked as intended. I couldnt find out though why is that so :/

You don't have to do anything special, Parallel.Foreach() will wait until all its branched tasks are complete. From the calling thread you can treat it as a single synchronous statement and for instance wrap it inside a try/catch.