Try this in the activity view in which you want the notifications to be seen : Games.setViewForPopups(getApiClient(), getWindow().getDecorView().findViewById(android.R.id.content));
The issue was that I was calling Games.Achievements.unlock(mGoogleApiClient, context.getResources().getString(R.string.achievement_pro)); from a helper class. The context that I passed was of MainActivity.class, however I actually intended to show the achievements being unlocked in my GameScreen.class and not the MainActivity.class since it would be in the background. GameScreen.class, in my case, is an activity that I invoke through an Intent from MainActivity.class. And I suppose, it is because of this that the context is not set properly for Games.Achievements and it could not show the pop ups in my current activity screen.
When I added that line of code in GameScreen.class, I assume that now Games class knew where it has to popup the alerts. My explanation might sound a bit fussy here but let me know if you have any issue.