“He is an experienced Premiership and international player and will fit into the way we want to play this season," Foxes boss Micky Adams told Leicester's official website.
“He plays wide on the right and has pace and skill. And at the age of 28 he still has a lot to offer.
"I think he will be a valuable addition to our squad. He will be having his medical today and, subject to that, will sign for us.”
Gillespie will become Adams' fifth signing of the summer joining Steve Howey, Riccardo Scimeca, Paul Brooker and Danny Coyne.