The 25-year-old has trained throughout the summer at Franklin’s Gardens as cover for the injured Sam Dickinson, playing in the pre-season friendlies against Rotherham, Leinster and Newport-Gwent Dragons.
A member of the England Under-20 team which reached the 2008 IRB Junior World Championship final, Fisher has also earned England Saxons honours, and has played on both the flank and number eight in his short time in black, green and gold.
Director of rugby Jim Mallinder said that Fisher deserves his chance after making a positive impression over the past few weeks.
“Jon is a talented player who will give us depth across the back row,” he said. “He has worked hard throughout our pre-season training, putting in plenty of effort in both conditioning and rugby sessions.
“More importantly he has shown that he has the determination to play and succeed here at Franklin’s Gardens, and we were delighted to offer him this contract.”
Fisher says that he is excited by the opportunity that has been offered to him by the Saints coaching team.
“I’ve had a great time at the Saints this summer, working with a superb group of coaches and outstanding players,” he said. “I had no hesitation in accepting Jim’s offer to join the squad full-time and am looking forward to helping the Saints maintain their place at the top of English rugby.”
The club also announced that lock Rob Verbakel has left the club over the summer, before the resumption of pre-season training.
