Mr Garrett said the Labor government had always intended to run its full term.
Ms Gillard in her agreement with independent NSW MPs Tony Windsor and Rob Oakeshott had settled on an election to be held in either September or October this year.
Senior government frontbencher Anthony Albanese said Ms Gillard had followed convention in not consulting with all party MPs on deciding on the election date.
"No prime minister has ever held a full caucus meeting, and has had a discussion when they think the election date should be," he told ABC TV on Sunday.
"It was obvious to anyone who had looked at it there were only two possible dates and the prime minister chose one of them."
Mr Albanese dismissed the notion the departure of senior ministers Chris Evans and Nicola Roxon had created instability for the government.
Senator Evans and Ms Roxon announced on Saturday they would quit politics this year.
"There is no suggestion other than personal ones and understandable ones," Mr Albanese said.
He said members of both parties had announced they would not stand at the 2013 election.
"There have been no less than nine coalition members (say) that they won't be standing at the next election," he said.
The cabinet reshuffle, which included promoting Mark Dreyfus QC to attorney-general and switching Chris Bowen from immigration to tertiary education minister, showed the depth in the government's ranks, Mr Albanese said.
"It is an orderly process whereby we have had very good replacements found for people who have been very good ministers," he said.
-AAP
