He played college football for the Michigan Wolverines, and was selected by the Patriots in the sixth round of the 2020 NFL draft.

[6] During the early portion of his rookie season, Onwenu played across the offensive line after injuries affected the normal lineup;[7][8] Onwenu took snaps as a sixth offensive lineman/jumbo tight end, at right tackle, and at both guard positions.

[10] Despite alternating between guard and tackle, Onwenu finished the year ranked as one of the best offensive linemen in the NFL and started in all 16 of the Patriots' games.

[13] After starting the first four games at right tackle, Onwenu switched back to right guard due to multiple injuries to the offensive line.

Onwenu is of Nigerian descent; his parents were born in Nigeria but later moved to the United States.