Helenius vs. Brewster

In January 2010 Helenius made the biggest step up so far of his professional career in squaring off against former WBO heavyweight champion Lamon Brewster. Many commentators wondered if the Brewster fight had come too early for the big Finn, however Helenius proved his toughness and punching power by grinding Brewster down to score a brutal TKO in the eighth round. Helenius went on to defeat Gbenga Oloukun on 26 March 2010 in Helsinki, despite breaking a bone next to the knuckles of his right hand.

In August 2010 Helenius won the vacant EU heavyweight title against unbeaten Grégory Tony. Helenius defended his title for the first time on 27 November 2010 by beating Attila Levin with a technical knockout in the second round. In the same match he also won the vacant WBO Inter-Continental title.

Helenius vs. Peter

Trying to build on the momentum of his big win over Lamon Brewster, Helenius signed to fight another former world heavyweight champion in Samuel Peter. Peter was coming off a brutal 10th-round knockout loss to unified heavyweight champion Wladimir Klitschko in their marquee rematch bout. The fight took place on 2 April 2011. Peter started the bout aggressively working behind a consistent body and head attack. However, Helenius weathered the storm and soon began to find the mark with his trademark right hand in the middle rounds. As the bout headed into the 9th the score cards were divided, nevertheless Helenius ended matters scoring a brutal knockout leaving Peter out cold on the canvas for well over the 10 second count.

Helenius vs. Liakhovich

On 27 August 2011 Helenius successfully defended his WBO and WBA Inter-Continental titles against Sergei Liakhovich in Munich, Germany, by technical knockout in round 9. It was Helenius' third knockout victory against former heavyweight champions and further cemented his position as one of the world's top ranked heavyweights.

Helenius vs. Chisora

On 3 December 2011, Helenius won the vacant European Championship title (EBU) by beating Derek Chisora by a twelve-round split decision in Helsinki, Finland. The decision was highly debated as most pundits and onlookers thought Chisora had done enough to get the decision. In the Finnish press Helenius claimed he had injured his right arm in the first round of the match, and was thus unable to use it fully.^[5] A fracture was found, but it was considered to be minor.^[6] The result was widely criticized by the crowd and pundits with Freddie Roach who was commentating the fight labelling it "just terrible" and added 'Helenius was supposed to be the next big thing and the man to challenge the Klitschko's, but Derek totally exposed him and I'm being generous in giving him four winning rounds in the fight'.^[7][8]

The Ring considered the outcome of the match "a gift", dropping Helenius' ranking from fifth to sixth challenger.^[7][8] On the other hand, his slugger fighting style has been described as lazy but powerful; he looks to be not doing much, but keeps putting men down.^[9]

The injury required an operation and to achieve complete healing and to minimize any possibility of further injury, a long break from fights. After a year away from boxing, Helenius beat veteran Sherman "The Caribbean Tank" Williams on points on 10 November 2012 in Helsinki keeping his clean record. The fight was the main event on the only Sauerland Events Viasat Nordic Fight Night card so far held outside of Denmark. On 23 March 2013 in Magdeburg, Germany, Helenius won his match against Michael Sprott on points in 10-round match. Helenius broke his right hand wrist in fight.^[10]

Due to contract disputes with Team Sauerland, Helenius was inactive for two years, before breaking off the contract with Sauerland in February 2015.^[11] Sauerland did not accept the one-sided break of contract and took the issue to the court.^[12]

Helenius vs. Whyte

On 15 October 2017, it was announced that Helenius would face Dillian Whyte on 28 October, after Whyte had had a hard time finding an opponent.^[25] Whyte controlled the match from the third round on and eventually won by a twelve-round unanimous decision.^[26] Helenius commented afterwards that he knew the risks for accepting the match on such fast notice and with only a week of training, but took the risk in a need for money.^[27]

On 17 March 2018, Helenius faced Yury Bykhautsou in Rakvere, Estonia. Helenius got injured during the match, but ended up winning by an 8-round split decision.^[28] Disappointed with his performance during the match, Helenius negotiated a rematch with Bykhautsou for 11 August 2018 in Olavinlinna.^[29] Rematch ended with Helenius landing another victory, this time by a unanimous decision.^[30]

Helenius vs. Teper

On 29 September 2018, Helenius faced Erkan Teper for the vacant IBF Inter-Continental heavyweight title. The bout consisted of Helenius controlling most the fight before knocking out Teper in round 8.^[31]

Helenius vs. Washington

After almost a year away from the ring, Helenius made his first appearance in the United States, facing Gerald Washington on 13 July 2019. He lost the bout via knockout in the eighth round.^[32]

On 30 November 2019, Helenius faced Mateus Roberto Osorio in Narva, Estonia. After dropping Osorio in the end of the first round, Helenius went on to knock him out via a body punch in the second round.^[33]

Helenius vs. Kownacki

On 7 March 2020, Helenius squared off against undefeated Adam Kownacki in a WBA title eliminator. While Kownacki was the heavy favorite, Helenius pulled off a significant upset by stopping Kownacki in the fourth round winning the vacant WBA Gold heavyweight title in the process. The victory lined up Helenius as the mandatory challenger for titlist Anthony Joshua.^[34] However, Joshua was already set to fight Kubrat Pulev and Kownacki exercised his contractual rematch clause.^[35]

Helenius vs. Kownacki II

According to Helenius' manager, the rematch was postponed several times due to various reasons and ultimately after over a year out of the ring, Helenius returned on 9 October 2021 on the main card of Tyson Fury vs. Deontay Wilder III, against Adam Kownacki.^[35][36] The bout was stopped after six rounds of dominance by Helenius against a clearly overpowered Kownacki. The former had inflicted his opponent with a swollen left eye, before suffering repeated low blows, which caused Kownacki to be disqualified in the sixth round.^[37] After the bout, the result was later changed to a technical knockout victory for Helenius.^[38]

Helenius vs. Wilder

Helenius then faced former WBC heavyweight champion Deontay Wilder with the fight scheduled to occur on October 15, 2022, at Brooklyn's Barclays Center.^[39] He lost the bout by first round knockout.^[40]

Helenius vs. Joshua

On 6 July 2023 Dillian Whyte vs. Anthony Joshua II, a rematch of the 12 December 2015 bout. was announced to be held at The O2 Arena in London. ^[41] This was cancelled on 5 August 2023, after Whyte returned a positive drug test conducted by the voluntary anti-doping agency.^[42][43] On 8 August 2023, Helenius was announced as the replacement for Whyte, with the bout taking place on the originally scheduled date of August 12, 2023.^[44][45][46] Helenius lost the bout by knockout in the 7th round.^[47]