How can I view my Photos library from within iMovie? I have no way of viewing all of the videos and photos taken on my iPhone, that is already syncing perfectly fine with Photos for OS X.
I might think that you actually have TWO Photos Libraries, one of them being empty AND selected as "System Photo Library".
Check your "Pictures" folder, open your actual Photos Library from here (double-click on it), then go to Photos Preferences / General, and click "Use as System Photo Library".
Quit and relaunch iMovie.
NB : I was able able to reproduce your problem by creating a new (empty) Photo Library and marking it as "System Library".
Thanks for the reply. It was already set as the default library:
[doublepost=1463311329][/doublepost]I managed to fix the problem.
I created a new photos library, set it as default, then opened iMovie and saw my photos. So I opened the original photos library, and then set that one as default and deleted the new library.