Onyemata is a native of Lagos, Nigeria, where he attended the Chrisland Schools but he graduated from Rainbow College.

Onyemata had never seen a gridiron football game until he came to Winnipeg, but he became a standout player for the Manitoba Bisons.

[8] In 2018, Onyemata played in all 16 games with four starts, recording 35 tackles, 4.5 sacks, and a forced fumble.

[11] In Week 9 against the Tampa Bay Buccaneers on Sunday Night Football, Onyemata recorded his first career interception off a pass thrown by Tom Brady during the 38–3 win.

[12] On March 3, 2021, Onyemata agreed to convert part of his $7 million base salary into a signing bonus to free up cap space for New Orleans.