Till was born in Liverpool, England and began training in Muay Thai at the age of 12. After dropping out of school aged 14, he turned professional a year later and began training in MMA with Team Kaobon aged 17. In August 2012, Till was stabbed twice in the back after confronting a large group of men at a party. The knife missed his main artery by a millimeter and doctors claimed he was lucky to be alive. Following the incident, his coach Colin Heron advised Till to move to Brazil to train with a former Team Kaobon coach to avoid troubles in his hometown.

Till was involved in a fight at a party in August 2012 and was stabbed twice in the back, after confronting a group of men.

Till was once involved in a stabbing incident that left him with two scars on his back. According to the 27-year-old Muay Thai stylist, he fought “multiple bouncers and patrons” at a club during a party in August 2012. Sensing that life in Liverpool, England, was detrimental to his development, Till’s coach advised him to move to Brazil to continue his training. He wound up staying in the South American country for three and a half years despite initial plans for a six-month stay.

Till spent most of his early MMA career in Brazil under the guidance of Astra Fight Team. He went 3–0 as an amateur in England before making the move to South America, and turned professional in February 2013. Till had 11 fights in Brazil and one in Argentina prior to joining the UFC, with just two going to a decision. In 2013, he fought eight times as a middleweight before competing at welterweight in late 2014.

Till faced Brazilian Wendell de Oliveira Marques in his UFC debut on nine days notice at UFC Fight Night 67 on 30 May 2015. Oliveira managed to control most of round one by pinning Till to the fence, kneeing him in the abdomen and the upper inner thighs. In round two, Till successfully completed an early shot and took Oliveira down, ending up on top where he rained down elbows. He knocked out Oliveira and secured his first UFC win.

Till next faced Nicolas Dalby on 24 October 2015 at UFC Fight Night 76. After a back and forth fight, the bout was scored a majority draw. Both participants were awarded the Fight of the Night bonus.

He subsequently joined Astra Fight Team in Balneário Camboriú, despite being unable to speak the language and with minimal knowledge of grappling. While Till planned to spend six months in South America, he stayed for three-and-a-half years and welcomed a daughter in Brazil. In late 2016, Till returned to England to be reunited with Heron at Team Kaobon. His daughter and then-girlfriend remained in Brazil, and in 2018, Till revealed he hadn’t seen his daughter for over a year.

After a significant shoulder injury and various personal issues kept him out of action for an extended period of time, Till returned to face Jessin Ayari on 28 May 2017 at UFC Fight Night 109. He missed the non-title Welterweight limit of 171 pounds by 5 pounds, and had to give 20 percent of his fight earnings to his opponent. He explained that he had missed weight due to his long lay off from competition and that his body had not responded as well to the weight cutting process as it had in the past. Despite this difficult road to the fight, Till outpointed Ayari on the scorecards to win a unanimous decision (30–27, 30–27, and 29–27).

On 1 August 2017, Till announced that he had signed a new, five-fight deal with the UFC.

Till faced Bojan Veličković on 2 September 2017 at UFC Fight Night 115. Till extended his undefeated streak via unanimous decision.

Till faced Donald Cerrone on 21 October 2017 at UFC Fight Night 118. He won the fight via TKO in the first round. This dominant win earned him the Performance of the Night bonus award.

Till faced former UFC Welterweight title challenger Stephen Thompson at UFC Fight Night 130 on 27 May 2018. At the weigh-ins, Till weighed in at 174.5 pounds, 3.5 pounds over the Welterweight non-title fight limit of 171. After negotiating with Thompson’s team, the bout proceeded at a catchweight with the stipulation that Till could not weigh more than 188 pounds on the day of the fight. Till also forfeited 30 percent of his purse to Thompson. Till won the close fight via unanimous decision. He outstruck Thompson 38 to 30 in terms of significant strikes and scored the only knockdown of the fight in the fifth round. Despite this however, 22 of 25 media outlets scored the bout in favor of Thompson.

Till was given the opportunity to face Tyron Woodley on 8 September 2018 at UFC 228, challenging him for the UFC Welterweight championship. He lost the fight via d’arce choke in the second round after being dropped by the champion. This was Till’s first loss in his MMA career.

Despite talks of a potential move up to Middleweight, Till stayed at Welterweight and faced Jorge Masvidal on 16 March 2019 at UFC Fight Night 147. Till lost the fight by knockout in the second round. Both participants were awarded a Fight of the Night bonus award.

On 21 April 2019, it was revealed that Till had been arrested in Tenerife, Canary Islands on 18 April after trashing a hotel room after he was asked to leave, and for also stealing a taxi cab while the driver was loading Till’s luggage into the trunk. Till and four other involved individuals were sentenced for a crime of damage and unauthorised use of a vehicle, and were fined approximately £10,000.

Till faced Robert Whittaker on 26 July 2020 at UFC on ESPN: Whittaker vs. Till. He lost the fight via unanimous decision, though many admired Till’s performance against a former title holder in Whittaker.

Till was scheduled to face Jack Hermansson on 5 December 2020 at UFC Fight Night 185. However, it was announced on 6 November that Till was forced to withdraw from the bout due to an injury. He was replaced by Kevin Holland.

On 4 November 2020, Darren tweeted in support of a user who had used a transphobic slur against a trans woman.