Mortimer, 22, will join the Roosters from the Parramatta Eels who have granted him a release.
Sydney Roosters recruitment manager Peter O’Sullivan believes Mortimer will be a valuable asset to the club.
“Daniel suits the Roosters style of play and with his ability to play five eighth or halfback, we see him playing a key utility role, adding great depth to our halves alongside the likes of Braith Anasta and Mitchell Pearce.
“Daniel is widely regarded as a quality person on and off the footy field and we are looking forward to watching him develop as part of our team over the coming seasons.”
A Dally M Rookie of the Year finalist in 2009, Mortimer’s recruitment is in line with the Roosters policy of signing young players with whom the team can grow.
Mortimer will officially join the Roosters when the squad begins pre-season training next month.