Coun Holland also insisted the decision had nothing to do with the ongoing controversy around the appointment of the council leader’s £80,000 policy adviser.
Splott councillor Luke Holland’s resignation was accepted by council leader Heather Joyce on Wednesday, 14 months since Labour took power at County Hall.
A cabinet reshuffle will be confirmed on July 25.
Coun Holland, Welsh Labour’s former head spin doctor, said he was leaving the £31,900 post as cabinet member for adult services and communications to pursue other career opportunities.
Coun Holland earlier this year initiated plans for an arms-length company to provide adult social care in the city, with proposals set to be unveiled in October.
Coun Holland said: “It’s certainly not a case of walking away.
“It’s just a good opportunity, when things are in a very positive place, for somebody else to come in at the same time as our new director will be coming in to take forward these reforms that I’ve started.”
His resignation comes a month after a controversy ignited over the recruitment of a new “head of cabinet office”, whose role includes advising Coun Joyce on policy and public relations.
Coun Holland was one of five councillors on the job’s cross-party appointment panel.
It’s understood he voted with two opposition councillors for a policy manager from a London borough to get the post – in contrast to Coun Joyce, who voted for an internal candidate.
The appointment has since stalled after law firm Hugh James was called-in to investigate a complaint by a Labour councillor against the Conservative’s David Walker, another panel member, alleging he had made a pre-determined decision.
“The head of cabinet office has got absolutely nothing to do with this decision and has got absolutely no bearing on the decision I’ve taken to pursue some other exciting opportunities in my professional career,” Coun Holland said.
Asked if Coun Joyce should remain leader for the four remaining years of this council term, he told the Echo: “Absolutely.
“Heather Joyce is our leader. She was returned as our leader only a few months ago and she will continue to do things that she has done since she has been there, with the support of the cabinet and Labour group.”