Speaking to the media to explain his decision, he said:
"The last few weeks of rest away from the game have given me a lot of perspective on the great privilege and honour I have had in representing and leading my country in the three formats of this wonderful game. It has been a rewarding, sometimes tough and other times a lonely road, but I would not replace the experience for anything, because it has made me the man that I am proud to be today 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 South African cricket to relinquish the captaincy in all formats."
When Du Plessis was rested for the T20 series against England, Quinton De Kock replaced him as captain and may well be in line to now lead the side in all formats of the game - having been appointed one day captain earlier this year. During his time as captain, Du Plessis hit 11 centuries - although he hasn't recorded one in the last year.
Du Plessis will remain an integral part of the team and will continue to play for South Africa in what he envisages to be an important role. While there were rumours he may retire, he said that the potential retirement period would be after the T20 World Cup later this year. He is one of the country's better T20 players - being just one of four South African cricketers to have hit a century in the format.
He first captained South Africa in a T20 series against New Zealand in 2012. Following this, Du Plessis was named permanent T20 skipper in 2013. Four years later, he assumed full-time captaincy of all three formats, replacing AB de Villiers.
South African cricket has been in somewhat of a downward slope in recent years with the under-performance at the 2019 ICC Cricket World Cup in England being one of the low points for the team. The change in captaincy is perhaps part of a wider plan for South African cricket to try to revamp itself and bring back the glory days. Furthermore, going by his statement regarding a "perfect world" in which he would like to lead the team in Tests for the rest of the season and also to the T20 World Cup, it feels like the decision to resign was not entirely of his own volition.
He was caught in the middle of racially motivated storm when he suggested that the cricket team "does not see colour" when it came to dropping players (the team had dropped Temba Bavuma from the test side). Although well meaning, it caused problems in a country where it is still a sensitive subject. By the looks of things Du Plessis' repeated run-ins with the board and his appeals to them to sort South African cricket out fell on deaf ears when it came to solutions but on perfect ears when it came to reasons why he shouldn't be a captain anymore.