DEWSBURY & Mirfield MP Paula Sherriff was one of 48 so-called Labour rebels who voted against £12bn of benefit cuts.
Ms Sherriff defied Labour’s acting leader Harriet Harman, who had urged the party’s MPs to abstain from Monday’s vote.
The cuts were passed by 308 votes to 124. A total of 184 Labour MPs abstained.
Said Ms Sherriff: “This was an incredibly difficult decision and not one that was taken lightly.
“Voting against the wishes of my own party was not something I envisaged myself doing when I was elected as an MP 11 weeks ago.
“But the Dewsbury constituency has pockets of high levels of deprivation and child poverty.”
Child tax credit will now be limited to the first two children in a family and Ms Sherriff added: “Child tax credits, as the title suggests, are intended for the child and the costs incurred for raising that child.
“A child does not choose when to be born, so why should a third or fourth child suffer as a result?”
She accused the Government of offering tax breaks to corporations and said hitting low-paid working families at the same time was wrong.
“Ultimately I had to make the choice to stand up for the people I was elected to represent,” she said.
“Tax credits have been proven to improve the lives of millions of families. To abstain would have been letting down many of my constituents.”
Batley and Spen MP Jo Cox abstained on the bill which brings in controversial benefit changes. She voted in favour of a earlier Labour amendment that would have derailed plans to limit child tax credit to two children.
The motion fell by 308 to 208 votes. The Welfare Reform and Work Bill was then passed by 308 to 124.
Mrs Cox hopes parts of the bill she disagrees with can be changed and said: “I will not support any measures that would plunge more children into poverty.
“In my view most of this bill is terrible news for sick or disabled people and families on low and middle incomes.
“There are, however, a minority of good elements to it, including measures to increase the number of apprenticeships and support for troubled families.”