Michael's father Tony Mmoh was also a professional tennis player who represented Nigeria and reached a career-high ranking of No.105.

He won the 2016 USTA 18s Boys' National Championship to earn a wild card into the main draw of the US Open.

In February 2016, Mmoh qualified for his first ATP-level tournament at Memphis by defeating fellow Americans Dennis Novikov and Bjorn Fratangelo.

He then lost in the first round to eventual finalist Taylor Fritz, the highest ranked American teenager at the time.

Following his fourth Futures title, Mmoh was awarded a wildcard into the Miami Masters, where he lost to Alexander Zverev, the top-ranked 18 year-old in the world, after dropping two tiebreaks.

In September 2016, Mmoh broke into the top 300 for the first time by reaching the final of the ATP Challenger event at Tiburon as a qualifier.

To start off the 2018 season, Mmoh recorded his first career ATP-level match wins by defeating Federico Delbonis in the first round of the Brisbane International and world No.

[6] At the 2018 Miami Open he reached the third round as a qualifier for the first time at a Masters level defeating 12th seed Roberto Bautista Agut for his first top-15 win and the biggest of his career.

In January 2019, Mmoh qualified for the first time via ranking in a Grand Slam main draw at the 2019 Australian Open where he lost in the first round to Radu Albot.

At the 2020 Australian Open, Mmoh recorded his first main draw victory with a straight sets win over Pablo Andújar as a wildcard.

In 2022, he entered the 2022 U.S. Men's Clay Court Championships as a lucky loser directly into the second round replacing top seed Casper Ruud who withdrew in the last minute.

422, Mmoh qualified for the main draw with a win over wildcard Georgi Georgiev at the 2025 Dallas Open, and then defeated Roberto Carballes Baena in the first round.