have a part in (something)

1. To have a specific involvement or participation in something. There's no use lying to the committee, Mr. Marshall, as we know for a fact that you had a part in hiding your company's losses from its investors. Look, we all have a part in making sure this campaign is successful, so we each have to do our best. I didn't have a part in this, Officer, I swear! I had no idea they were stealing money!

2. To have a job portraying a certain character in a performance, such as a play or a film. I hear that Samantha has a part in some new film. She's really making her way into the big leagues! I bombed my audition, so I'm not surprised I don't have a part in the play. There are plenty of people in Hollywood who've never had a part in anything, despite going to lots of auditions.