Connell appointed Mullins as his number one at the end of January last year and the pair enjoyed top-flight success last season, with The Tullow Tank winning the Royal Bond at Fairyhouse and the Future Champions Novice Hurdle at Leopardstown.
Foxrock was another significant multiple winner for the combination, but Connell has decided the time is right for a change.
He said: “It’s purely a business decision. We just took a review of the last six months or so and I’ve decided I’d like Adrian to ride for me.
“Danny is a good personal friend of mine and remains a good personal friend and it is just a business decision.
“Adrian has never ridden for me before, but he comes highly recommended.
“He will probably have his first ride for me on a horse called King Schultz in a maiden hurdle at Thurles on Thursday.”
Heskin (pictured), who won the bet365 Gold Cup at Sandown four years ago aboard Church Island and tasted Cheltenham Festival success with cross-country winner A New Story in the same year, is excited by the formation of a new partnership.
Heskin said: “I’m absolutely delighted, and very grateful to have been given the opportunity.”