The former Houston Dynamo forward and son of Liverpool legend Kenny Dalglish spent two years as head coach of the Aztex when the club was part of the USL's development league. Dalglish coached Austin to the 2013 USL PDL Championship and was named the 2013 USL PDL coach of the year before joining RSL.
Austin was introduced as USL PRO's newest expansion franchise in June and will begin competing in the league in 2015. Dalglish will resume his role as head coach and technical director.
Real Salt Lake has begun its search to replace Dalglish and expects to make a hire within the week.
"I will be sad to leave the fantastic players and staff that have become friends behind in Salt Lake City," Dalglish said in a statement. "They have made me a better coach and a better person. The challenge of leading the Aztex in their inaugural year in the professional ranks was one I couldn't refuse."
Dalglish, whose primary responsibility was to coach RSL's forwards, told The Tribune during the preseason that he and his wife who is from Texas were happy in Austin. He added that a special opportunity was necessary to take him away from the Aztex.
"It's not very often that you get the chance to work alongside a head coach like Jeff and for an organization like Salt Lake," Dalglish said at the time. "In Austin, I always told myself, it wouldn't be just for a club, it would be for the people and after I met with Jeff and Garth [Lagerwey], I met good people."
The 37-year-old Scotsman said his fondest professional memories were in Texas. He also met his wife there, and their two children were born in the Houston area.
"Texas is home for me in America," Dalglish said.