Onyemata was selected by the New Orleans Saints in the fourth round of the 2016 NFL draft as the 120th overall pick.[5] He was the first player from the University of Manitoba ever selected for the NFL draft, and the twelfth NFL draft pick from the CIS (now U Sports). The Saints traded their fifth round picks for 2016 and 2017 to Washington in order to draft Onyemata.[6][7] He was also selected by the Saskatchewan Roughriders in the fourth round of the 2016 CFL Draft.[8]
In 2018, Onyemata played in all 16 games with four starts, recording 35 tackles, 4.5 sacks, and a forced fumble.[9]
Onyemata was suspended the first game of the 2019 season for violating the league's substances of abuse policy.[10] He was reinstated to the active roster on September 10, 2019.
On March 18, 2020, Onyemata signed a three-year, $27 million contract extension with the Saints.[11]
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. On July 16, Onyemata was suspended six games by the NFL after testing positive for a banned substance.[13]
Atlanta Falcons
On March 16, 2023, Onyemata signed a three-year, $35 million contract with the Atlanta Falcons, reuniting him with his former Saints position coach, Ryan Nielsen, who was named the Falcons defensive coordinator.[14]