Heinisch, who is a Colorado native, was diagnosed with ADHD when he was young. His parents home schooled him and placed him in wrestling classes as he had too much energy and could not pay attention in school. He won the Colorado state high school championship and was an All-American twice. He went on to wrestle at North Idaho College but dropped out of school and started selling ecstasy pills to keep up with his lifestyle after his parents lost their house and got divorced. He was arrested for selling 2,000 ecstasy pills and headed to Amsterdam to avoid a jail sentence after meeting bail. He ended up working in a bar in Spain and sleeping on the beach for three months. Not long after Heinisch started drug tracking from South America to Spain and got caught on one of his trips when a Spanish immigration officer found one kilo of cocaine on him. Heinisch ended up in prison at Canary Islands. He taught himself how to speak Spanish by reading a Spanish bible with an English dictionary and taking up boxing. After he finished serving his prison sentence in Spain, Heinisch flew back to New York where he was apprehended upon re-entry to United States for fleeing the country back in 2009. He changed his life around after finishing his sentence at Rikers Island in the United States and pursued an MMA career.
Heinisch started his professional MMA career in 2015 and fought under various promotions, namely Sparta Combat League, and Legacy Fighting Alliance where he was the interim middleweight champion after defeating Gabriel Checco and was promoted to middleweight champion after Anthony Hernandez vacated the title in June 2018 when he signed with the UFC. He amassed a record of 10-1 prior to competing in Dana White's Tuesday Night Contender Series.
Heinisch appeared in Dana White's Tuesday Night Contender Series Dana White's Tuesday Night Contender Series - Season 2, Episode 7 web-series program on July 31, 2018, facing Justin Sumter. He won the fight via knockout in the first round and was signed by UFC.
Heinisch made his UFC debut on November 17, 2018 against Cezar Ferreira, replacing injured Tom Breese at. He won the fight via unanimous decision. His next fight came on May 18, 2019 at against Antônio Carlos Júnior He won the fight via unanimous decision. Heinisch faced Derek Brunson on August 17, 2019 at UFC 241. He lost the fight via unanimous decision. Heinisch was expected to face Brad Tavares on October 26, 2019 at UFC on ESPN+ 20 However, Heinisch was removed from the pairing in early October for undisclosed reasons. In turn, Tavares was removed from the event entirely and rescheduled to face Edmen Shahbazyan a week later at UFC 244. Heinisch faced Omari Akhmedov on December 14, 2019 at UFC 245. He lost the fight via unanimous decision. On March 31, 2020, Heinisch revealed that after fighting out his contract, Heinisch signed a new, four-fight contract with the UFC. Heinisch was scheduled to face Gerald Meerschaert on June 6, 2020, at UFC 250, however two days before the fight his cornerman tested positive for COVID-19. Heinisch was pulled from the fight and replaced by promotional newcomer Anthony Ivy. Subsequently, the cornerman was re-tested and the initial test was proven to be false positive and Heinisch was reinstated to the card. Finally, Heinisch faced Meerschaert as originally scheduled and won the fight via TKO in the first round. Heinisch targeted a quick turnaround and was scheduled to face Brendan Allen on June 27, 2020 at. However, Heinisch pulled out of the matchup in mid-June citing an injury and was replaced by promotional newcomer Kyle Daukaus.
