The left-back arrives as a free agent, having left Walsall in the summer.
Starting his career in Scotland, Leahy made 158 appearances for Falkirk across five seasons, making his debut in the 2012-13 season, when Falkirk gained promotion to the Scottish Championship.
In 2017, the defender joined Walsall and was a constant feature of the side throughout the campaign, making over fifty appearances and contributing three goals.
Appearing forty times in Sky Bet League One last season, Leahy contributed heavily to his side’s attacking intent from full-back, providing a number of assists throughout the season and scoring three times.
Speaking about the signing of the versatile defender, Manager Graham Coughlan said “Luke is a player we’re very pleased to have at the club.
“He’s got two League One seasons under his belt, so his experience there will be a great asset going forward.
“What’s particularly impressive about Luke is his ability to have an impact further up the pitch, he is great defensively, but also his assist statistics speak for themselves.
“Between him, Michael Kelly and Tareiq Holmes-Dennis, we’ve got a lot of choice on the left side of the defence, so I’m pleased to have that kind of squad depth at my disposal.”