Reilly arrived through the youth ranks of Dumfries club Queen of the South, signing a professional contract before the start of the 2010–11 season.
[3] He made his competitive first-team debut on 31 July 2010, in a 5–1 Scottish League Cup first round win versus Dumbarton as an 83rd-minute substitute for Derek Holmes.
[6] On 23 June 2015, it was announced that Reilly had signed a three-year contract with Scottish Premiership club Heart of Midlothian, with an undisclosed development fee being paid to Queen of the South.
Reilly's first appearance for the Pars was in a 3–0 victory at East End Park in the Scottish League Cup[11] and his first goal arrived in a 2–1 defeat away to Hibernian at Easter Road.
Reilly left St Mirren at the end of the season when new manager Alan Stubbs opted to withdraw the offer of a new contract.
[25] On 24 May 2022, Reilly returned to Dumfries club Queen of the South on a two-year contract, despite the Doonhamers relegation to Scottish League One at the end of the 2021-22 season.