The 19-year-old, who made 19 first-team appearances during the 2012/13 campaign, originally had a one-year option implemented in April
However the Republic of Ireland U21 international has now put pen-to-paper on a new two-year deal keeping him at St. Andrew's until 2015.
Solihull-raised Reilly is a product of the Blues Academy having joined the club at the age of seven. The talented teenager made his first-team bow during the FA Cup fourth-round victory over Sheffield United in January 2012 and bagged his first senior goal at Huddersfield Town in January 2013
A full BluesTV
interview with Reilly will follow on bcfc.com.