Agar has been working as head of player pathways at NRL club St George-Illawarra Dragons since leaving Warrington Wolves, where he was assistant to coach Tony Smith, a year ago.
He is joining Rhinos in a new role created following a backroom shakeup which was announced last week.
His responsibilities will include overseeing Rhinos’ academy, scholarship and women’s sides along with talent identification, coach education and community club partnerships.
Agar, 46, will manage department heads Simon Bell, Rob Burrow, Jonny Wainhouse, Mark Butterill and Barrie Eaton and also oversee parts of the Leeds Rhinos Foundation’s Rugby league development plan for Leeds which relates to elite young player and coach development.
He said: “I am delighted to be joining the Rhinos.
“I would like to thank everyone at St George-Illawarra for the support they have given me and I am looking forward to this new challenge with Leeds.”
Rhinos’ director of rugby Kevin Sinfield commented: “Richard is an ideal candidate for this new position given his vast experience both in Super League and over in the NRL.
“Our player development programme is vital to our progress as a club and having a person of the calibre of Richard overseeing that is a major boost for the Rhinos.”
Bob Bowman, chief operating officer for Leeds Rhinos Foundation, added: “We are delighted to have attracted someone like Richard who has vast experience in top line coaching, coach education and management.
“He will be a big asset for us.”
Agar played as a half-back for Featherstone Rovers, Dewsbury Rams, Widnes Vikings and Rochdale Hornets.
He began his coaching career as an assistant at Featherstone and was in charge of York before moving to Hull as second in command.
He was head coach there from 2008-11 before three years in charge at Wakefield.