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.