As part of a restructure of the council's children and young people's services, youth workers will be placed in multidisciplinary district teams.
Rittman's post will be replaced by the post of central strategic manager for youth and community services. Rittman, who is executive member of the Association of Principal Youth and Community Officers (APYCO) for the South, is leaving because the new role does not involve direct delivery of youth work.
"In Hampshire youth work is key to the development of district teams," he said.
Rittman, 56, has headed the youth service for nearly nine years. He plans to set up a management consultancy. Carole Aspden, principal youth officer for West Sussex, will replace him at APYCO.
See Leader, p13.