Symons left his national role in July 2015, midway through their Euro 2016 qualifying campaign, to concentrate on his job as Fulham manager, but has since been sacked.
Former Wales international Tony Roberts, currently at Swansea City, will replace Martyn Margetson as Wales' goalkeeping coach.
Margetson is leaving his Wales role to work for England and Sam Allardyce.
Paul Trollope has relinquished the role that Symons is retaking in order to concentrate on managing Cardiff City in the Championship.
Trollope succeeded Russell Slade as Cardiff boss in May.
Symons, 45, a former Portsmouth, Manchester City, Crystal Palace and Fulham defender had been Coleman's assistant on a match-by-match basis since 2012.
After being sacked by Fulham in November 2015, Symons was part of Coleman's scouting team at the European Championships in France, where Wales reached the semi-finals.
Wales begin their 2018 World Cup qualifying campaign at home to Moldova on 5 September in Cardiff.
Kit Symons has returned to the Wales coaching set-up under Chris Coleman.