Mr Cunliffe has made it abundantly clear in public statements that had Mr Robertson wanted to be his second in command he would have recommended him for the sake of party unity.
Instead Mr Robertson has opted for a role as shadow Leader of the House, Mr Cunliffe confirmed.
Until now that has been undertaken by senior MP Trevor Mallard - currently in San Francisco watching the America's Cup.
Mr Parker will remain Labour's finance spokesman.
Cunliffe supporters Sue Moroney and Ian Lees-Galloway have been elected senior and junior whip respectively, replacing Robertson loyalists Chris Hipkins and Darien Fenton.
Mr Robertson's decision to stay out of Mr Cunliffe's leadership team has already sparked suggestions that divisions between Mr Robertson's supporters and Mr Cunliffe have not healed.
Prime Minister John Key told reporters at Parliament the decision showed "shows how deep the rifts are within the Labour Party caucus".
"In the end if they were really a united caucus they needed to bring the two parts of the equation together and essentially they've failed to do that.
"What that shows you is the Robertson camp isn't really backing David Cunliffe so that will spell problems for him over time."
Mr Cunliffe won the three-way leadership contest on Sunday against Mr Robertson and Shane Jones, but Mr Robertson won much more support in the caucus, 16 votes to Mr Cunliffe's 11 and Mr Jones' seven.
Mr Robertson and Mr Cunliffe met yesterday to discuss their preferences and both said the decision was mutual.
Mr Cunliffe spoke to reporters at Parliament before today's caucus meeting, flanked by Mr Robertson, Mr Jones, Mr Parker and President Moira Coatsworth.
"Today we are joined together. We are putting the party first," Mr Cunliffe began.
Mr Robertson's talents would be used as the "spearhead" in the House.
"We are both very comfortable about where we have got to on that."
Mr Cunliffe said Mr Parker, Mr Robertson and Mr Jones would all be part of a strong economic and employment team.
Mr Robertson said he and Mr Cunliffe had come to a "consensus" that the proposed line-up was the strongest possible "and I absolutely endorse and support it".
Mr Parker is a Dunedin-based list MP. He played his cards very close to his chest during the latest leadership contest although it is thought he voted for Mr Jones.
He was a senior minister in Helen Clark's Government, holding the portfolios of climate change issues, energy and state services, and was Attorney-General.
He took over as finance spokesman from Mr Cunliffe in December 2011 when the leadership changed from Phil Goff to David Shearer.
Mr Parker had originally thrown his hat into the ring as a leadership contender with Grant Robertson as his deputy after Mr Goff stepped down. He withdrew when Mr Shearer stood and Mr Robertson indicated he would back Mr Shearer over Mr Parker.
- Audrey Young of the New Zealand Herald
