Right-back Darby was captain of the victorious Liverpool side in the FA Youth Cup in 2006. He made the move from the Academy to Melwood during the summer of 2006. His opportunity finally came in the closing minutes of a defeat to Tottenham in the League Cup at White Hart Lane in the middle of November 2008. Although ‘on the bench’ for four Premier League matches during the 2008/09 season, the only other game in which Darby got some playing time came in a European fixture against PSV Eindhoven in Holland when he replaced Álvaro Arbeloa. The official Liverpool Supporters Club handed Stephen Darby the “Ian Frodsham young player of the year” award in recognition of both the progress he had made on the pitch during 2008 and the excellent way he conducted himself off it. Darby signed a new contract with the club in July 2009, but following only three appearances in the ensuing season he was loaned to Swindon Town in League One in March 2010. Darby played in 12 League games as Swindon finished fifth and qualified to meet Charlton Athletic in the play-offs. Each club won its home leg 2-1 and the tie went to a penalty shoot-out in which Darby secured Swindon’s progress into the play-off final. Darby came on as a substitute for Swindon Town in the League One final against Millwall, but the Wiltshire club lost 1-0. The 23-year-old was released by Liverpool in the summer of 2012 and signed a two-year deal with Bradford City in League Two.
Darby was a regular for Bradford City'in 2012/13 and a member of the Bantams team that played against Swansea City in the League Cup final at Wembley in February. Although heavily defeated on that day, Bradford returned to Wembley in May in the League Two Play-off final and Darby again played from start to finish as Northampton were beaten 3-0 to ensure his club's promotion to League One. Darby played in all 46 League One matches for Bradford City in the 2013/14 season. that ended with promotion. City finished the season in 11th place. Stephen was a multi-award winner at his club's end-of-season dinner in May 2014 and was made club captain in the summer. In the following two seasons he missed just one league game and after being released in the summer of 2017 stepped up a division, joining Bolton in the Championship.In September 2018 Darby accounced his retirement from the game at the age of 29 as he had been diagnosed with MND. “It is with great sadness that I announce my immediate retirement from professional football due to a recent diagnosis of motor neurone disease,” said Darby in a statement released by Bolton..“I would like to take the opportunity to thank my teammates, Phil Parkinson and all the staff at Bolton Wanderers Football Club for their amazing support at what has been an extremely difficult period for myself and my family. I would like to ask for privacy at this time so I can adjust to the battle I have ahead and so that I can spend time with those closest to me.” Darby was club captain at Phil Parkinson's Bolton. "This is heartbreaking news for Stephen and his family," said Parkinson. “He is an outstanding professional and a fantastic person. The Bolton Wanderers fans didn’t see the best of him due to limited first team opportunities, but I can assure everyone that he made a significant contribution in last year’s survival."