The midfielder is a product of Blues' Academy.
Born in Warrington but brought up in Solihull, he has been with the club since the age of seven.
Reilly made his first team debut as a second-half substitute during Blues' FA Cup with Budweiser fourth round victory against Sheffield United in January 2012.
He signed a one-year professional contract ahead of the 2012–13 season and went on to make 19 appearances during his first campaign.
His first senior goal came in a 1-1 draw against Huddersfield Town in January 2013.
In the summer of 2013 the Republic of Ireland U21 international signed a new two-year deal with the club.
On 11 March 2015, Reilly joined League Two side Burton Albion on an emergency loan. Unfortunately he made just two appearances for the Brewers before suffering a calf injury.