President Tabare Vazquez on Thursday vetoed a bill decriminalizing abortion passed earlier this week by Congress, said Tourist Minister Hector Lescano.
The Senate and House of Deputies lack the three-fifths required vote to override the veto, he added.
"In the next few hours, the legislative power will be notified, but what's certain is that (the veto) has already been signed and recorded. It's an irreversible fact that underscores the president's determination," Lescano told AFP.
The bill, hailed by some lawmakers as a milestone, would allow women to end their pregnancy in the first 12 weeks of gestation because of economic, family or age reasons.
In addition, abortion would be legal for health, deformation or risk to the mother's life.
The Roman Catholic church voiced "deep discomfort" with the bill it considered tantamount to legalizing the death penalty and said anyone who participated directly in stopping a pregnancy would be excommunicated.
Vazquez, also a doctor by profession, had announced that he would veto the Law of Sexual and Reproductive Health, because it included elements "with which I disagree, philosophically and biologically."
Some ruling party lawmakers tried but failed to win Vazquez's support for the bill that would have lifted a 70-year ban on abortions. They also failed to get his support in proposing a referendum on the measure.
A recent poll showed 57 percent of Uruguayans support access to abortion while 42 percent oppose it.