The Pitch Perfect 2 star celebrated the milestone at an unexpected bash organised by her pals, and Steinfeld posted photos from the party on on Sunday (14Jun15).

She added the caption, "I had the best night of my life last night with my favorite people, who threw me a surprise graduation celebration. We danced, karaoke-d (screamed, really) I laughed until I CRIED. Not really. But actually though. Thank you to everyone who came, I love you."

Fifth Harmony's Ally Brooke, model Alli Simpson and celebrity blogger Jared Eng joined pop star couple Mahone and Becky G at the party.

Steinfeld was also given a surprise from bosses at music label Republic Records, who presented her with a special cake in honour of her graduation.

She posted a snap of the dessert and wrote, "My @RepublicRecords family got me this... #GraduatedHighSchoolandSignedaRecordDeal."

Steinfeld signed the deal last month (May15), and is currently in the process of recording her debut album.