Huge majorities sided with Fitzpatrick, by counts of 95-3 in the Senate and 326-90 in the House, even though lawmakers in both parties, including Fitzpatrick, voted in December to approve the budget deal that included the pension cuts.
The few critics who spoke out against the repeal said the reversal was an example of lawmakers ducking a difficult choice - one that members of both parties supported less than two months ago.
"I've been down that road of trading spending increases today for spending cuts later many times - it doesn't work," said Sen. Jeff Flake (R., Ariz.). When deficit reduction plans pass, he added, "surely at some point we need to stand by them."
The measure approved in December was a small piece of a major compromise intended to end Washington's recurring budget fights.
The plan would decrease by 1 percent the annual pension increases for military retirees until they turn 62. Supporters said the change would affect retirees who are still of working age, and often in second careers, and free money for training and preparedness.
Critics said Congress was turning its back on veterans.
For former enlisted personnel, the average retiree would lose $69,000 in lifetime retirement benefits and receive a total of about $1.67 million in lifetime retirement pay instead of $1.73 million, according to the nonpartisan Congressional Research Service.
The White House is "supportive" of protecting current pension recipients, spokesman Jay Carney said this week.
U.S. Rep. Paul Ryan (R., Wis.), the former GOP vice presidential nominee and an author of the budget deal, said Fitzpatrick's plan "undermines" that agreement. "Rather than making the tough choices, it sidesteps them," he said in a statement.
Fitzpatrick responded: "It's never wrong to keep our promises to our nation's veterans."