Announced alongside ex-Hearts, Morton, and Queen of the South striker Gary Oliver, Mackie has signed a two-year deal with the League One side, teaming up with John McGlynn who took him on loan at Raith Rovers last season.
The Falkirk boss said: “We signed Sean for Raith in February and he just got better and better, he didn’t play much the season before due to injury but certainly showed how good he was both in defence and in attack.
“He’s very strong physically, got good pace, got energy and drive to get up and down the pitch, with a quality left foot, and at 23 we believe his best years are still ahead of him. We’re convinced he will be a great asset to the club.”
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McGinn, 33, has signed a one-year deal with the option of a second.
McGlynn added: “Stephen joins the club after a very successful season winning the championship with Kilmarnock, playing 40 games last season and a pivotal role in the Killie midfield. He brings huge experience to the club – as we all know, he comes from a famous footballing family, and we believe that his winning mentality will be key to getting the best out of his teammates.
“He’s good on the ball, obviously at his age he has great knowledge of the game but speaking with him he still wants to learn and play with an ambitious club.”