The new ACT Party leader denies he was overruled with the decision that his predecessor Rodney Hide will retain his ministerial portfolios.
Dr Brash, a former leader of the National Party, took over the ACT leadership from Mr Hide at the weekend.
On Tuesday, he announced ACT's rejigged ministerial responsibilities at a news conference in Wellington.
John Boscawen will stay on as deputy leader of the party, but will head the parliamentary caucus as Dr Brash is not an MP.
Mr Boscawen will relinquish his Consumer Affairs and Commerce portfolios.
Dr Brash has made it clear in the past he did not want Mr Hide in any position of prominence within the party.
However, he says Mr Hide is an effective minister and that there are still two very important pieces of legislation he has to progress.
Dr Brash says he was not rolled by the caucus on this issue, but the agreement was made after taking soundings from the caucus members on Tuesday.
Prime Minister John Key says he is happy to have Mr Hide stay on as a minister.
Mr Hide, the MP for Epsom, says he will retire from politics at the election in November.
Labour Party leader Phil Goff says it appears Mr Hide has done a deal to keep his ministerial portfolios and describes the situation as a shambles.
PM not ruling out finance role post-election
The Prime Minister has not ruled Dr Brash becoming finance minister after the election.
Last week, Mr Key said he could become a minister after the election, but it was highly unlikely he would get a finance role.
However, the Prime Minister did not rule this out when questioned by Labour Party MP Trevor Mallard in Parliament on Tuesday.
Brash allowed to sit in Debating Chamber
On Tuesday, Dr Brash took a seat in the Debating Chamber, even though he is not an MP.
Parliament's rules allow former MPs an observer's seat on the floor of the House.
Dr Brash sat alongside the Labour frontbench and left quickly when Labour MPs started asking the Prime Minister questions about him.