Kennedy made his début for the Blades in May 2011, coming on as a substitute in the last game of the 2010–11 season against Swansea City at the Liberty Stadium. Much was expected of Kennedy heading into his second season as a professional with the Blades, but due to a recurring knee problem he missed the majority of the campaign and didn't make a single appearance. After an intense rehabilitation period, Kennedy made his first start for the Blades in away game against Doncaster Rovers on 1 January 2013. Despite only making one appearance during the previous season, Kennedy had had his contract with the Blades extended in June 2013. Upon signing a new contract, Kennedy stated "I’m happy to sign a new deal at United... Hopefully, I’ll be able to repay the club, both this season and in the future, for the faith they’ve shown in me."