After playing collegiately at the
University of California, Berkeley, Onumonu was drafted by the
Boston Breakers with the 8th overall pick in the
2017 NWSL College Draft. She appeared in 18 games for Boston in her rookie season. She was waived on 8 May 2019, after playing in eight games. After stellar performances, she earned a supplemental roster spot on 28 June. On 17 January 2020, Onumonu was traded to
Sky Blue FC. She re-signed with the team on a one-year deal on 20 January 2022 based on her strong performance during the
2021 NWSL season, which saw her named to the Best XI Second Team. On 25 October 2022, Onumonu signed a new three-year contract that would keep her with Gotham FC through the 2025 season. On 30 December 2023, Onumonu was traded to
Utah Royals for $40,000 in allocation money. On 9 September 2024,
Montpellier HSC announced that they had signed Onumonu as a free agent. Onumonu announced her retirement from professional football via social media in October 2025. ==International career==