The 22-year-old striker came through Millwall’s youth ranks before signing a three-year-deal with Bolton Wanderers in the summer of 2013.
However, with first team opportunities limited, Conor spent time out on loan at several clubs including Oldham Athletic, Newport County, Barnsley and Chesterfield.
During his time at the Spireites he scored twice against the Gills, those goals coming in the entertaining 3-3 draw at the Proact Stadium last September.
In addition he has represented the Republic of Ireland at U17, U19 and U21 level, scoring twice in a total of 19 international appearances.
Speaking to the club’s official website Conor said: “I’m delighted to get it over the line; it’s been going on for a while now so it’s nice to get here and sign everything.
“Ady and Peter spoke very highly of the club and now I’m just looking forward to pre-season and getting up to speed.”