Early career

Omielańczuk made his professional debut in 2009, competing primarily in regional promotions across the Eastern Europe, including KSW, where he compiled a record of 15–3 before signing with the UFC in the spring of 2013.^[3]

Ultimate Fighting Championship

Omielańczuk made his promotional debut against fellow newcomer Nandor Guelmino on September 21, 2013, at UFC 165.^[4] After a back and forth first two rounds, Omielańczuk won the fight via knockout in the third round.^[5]

Omielańczuk faced Jared Rosholt on April 19, 2014, at UFC Fight Night 39.^[6] Rosholt defeated Omielańczuk via unanimous decision.^[7]

Omielańczuk was expected to face Soa Palelei on November 8, 2014, at UFC Fight Night 55.^[8] However, Omielańczuk was forced to pull out of bout with a broken thumb and was replaced by Walt Harris.^[9]

Omielańczuk faced Anthony Hamilton on April 11, 2015, at UFC Fight Night 64.^[10] Omielańczuk lost the fight by unanimous decision.^[11]

Omielańczuk was expected to face Konstantin Erokhin on July 18, 2015, at UFC Fight Night 72.^[12] However, Erokhin pulled out of the fight in late June citing an injury and was replaced by promotional newcomer Chris de la Rocha.^[13] He won the fight via TKO in the first round.^[14]

Omielańczuk faced Jarjis Danho on February 27, 2016, at UFC Fight Night 84.^[15] He won the fight via technical majority decision after Danho was hit with an inadvertent groin strike in the third round that rendered him unable to continue.^[16]

Omielańczuk next faced Alexey Oleynik on July 13, 2016, at UFC Fight Night 91.^[17] He won the fight via majority decision.^[18]

Omielańczuk faced Stefan Struve on October 8, 2016, at UFC 204.^[19] He lost the back and forth fight via submission in the second round.^[20]

Omielańczuk faced Timothy Johnson on March 18, 2017, at UFC Fight Night 107.^[21] He lost the back and forth fight by split decision.^[22]

Omielańczuk faced Curtis Blaydes on July 8, 2017, at UFC 213.^[23] He lost the fight by unanimous decision.^[24]

Absolute Championship Berkut

After his third consecutive loss, Omielanczuk was released from the UFC. He later signed with Absolute Championship Berkut, competing against American Bobby Brents at ACB 83: Baku in 2018. He won via first-round submission. After picking up a unanimous decision win in the regional kickboxing circuit, Omielanczuk returned to MMA to face Amir Aliakbari at ACB 89: Krasnodar in September 2018. He was defeated via unanimous decision.

Since the loss to Aliakbari, Omielanczuk has won his last four fights pushing him to 5-1 after leaving the UFC. He fought for the vacant ACA Heavyweight Championship against Tony Johnson at ACA 114: Omielańczuk vs. Johnson. He lost the fight by KO in the first round, marking the first time he has ever lost by strikes.^[25]

Omielańczuk faced Daniel James on April 23, 2021, at ACA 122. He won the bout via unanimous decision.^[26]

Omielańczuk faced Evgeniy Goncharov on September 11, 2021, at ACA 128. He lost the bout via TKO in the third round.^[27]

Omielańczuk faced Adam Bogatyrev on February 26, 2022, at ACA 136: Bukuev vs Akopyan. He lost the bout via unanimous decision.^[28]

Konfrontacja Sztuk Walki

Omielańczuk faced Ricardo Prasel at KSW 70 on May 28, 2022. He lost the bout via ankle lock in the first round.^[29]

Omielańczuk faced Michal Martínek on October 14, 2022, at KSW 75: Ruchała vs. Stasiak. He controversially won via split decision,^[30] with KSW paying Martinek his show money + his contractual bonus and, upon an official appeal from Martinek’s Team submitted, a full independent review of the decision was undertaken.^[31]

Omielańczuk faced Michał Kita on February 25, 2023, at KSW 79, losing the bout via ground and pound TKO in the third round.^[32]