The 35-year-old insists he needs to step back from the responsibilities that come with captaincy in order to help usher in the next generation of leaders for the Proteas.
Quinton de Kock will lead the side moving forward, allowing Du Plessis to concentrate his efforts as solely a batsman and a senior player.
“When I took over the leadership, I did so with the commitment to lead, perform & most importantly, to serve,” Du Plessis said in a statement.
“As the team heads into a new direction with new leaders and a young crop of players, I feel it will be in the best interests of SA cricket to relinquish the captaincy.
“This was one of the toughest decisions to make, but I remain fully committed to supporting Quinton, Mark and my teammates as we continue to rebuild and re-align as a group.
“The last season of my captaincy has been the most challenging to date as I had a lot of off-field issues that I devoted my energy towards.
“I have strived to lead the team with dignity and authenticity during exhilarating highs and devastating lows. I have given my everything during my tenure.
“South African cricket has entered a new era. New leadership, new faces, new challenges and new strategies.
“I remain committed to play in all three formats of the game for now as a player and will offer my knowledge and time to the new leaders of the team.”
De Plessis will remain part of the leadership group and offer guidance and advice when necessary.