Labour's 10p tax rebel Frank Field has apologised to the PM for "allowing my campaign to become personal".
The ex-minister said on Sunday Mr Brown was prone to "rages", was "unhappy", adding he would be "very surprised" if he was still Labour leader in 2010.
He apologised after Chancellor Alistair Darling set out tax allowance changes to MPs in the House of Commons.
Mr Field, who had threatened to step up his rebellion, congratulated Mr Darling "for putting an end to this issue".
Mr Field, widely reported to have fallen out with Mr Brown nearly a decade ago, led the backbench revolt against the axing of the 10p tax rate, which left 5.3m lower earning households worse off.
'Regret'
His personal attack on Mr Brown came in a BBC World Service interview on Sunday and prompted Schools Secretary Ed Balls to question whether Mr Field's motives were honourable.
Amid boisterous scenes in a packed Commons as the tax changes were announced, there was a hush as Mr Field got to his feet.
Mr Field welcomed Chancellor Alistair Darling's compensation package for those hit by the axing of the 10p tax rate and congratulated him "for putting an end to this issue".
He then added: "As the prime minister is in his place, might I also add that over the weekend I allowed my campaign to become personal. I much regret that and I apologise without reservation."
Mr Darling responded: "I'm grateful for what you said in both respects.
"I may say, it is not every day that honourable members have the courage to say what you said and it is appreciated."
Bookmark with:
What are these?