The amendment sponsored by the conservative Alabama senator, Jeff Sessions, would construct a three-layer fence along 600 kilometres of the lengthy border.
It would also see the construction of barriers to block vehicles on about 800 kilometres of border. The measure passed in an 83-16 vote.
"By passing my amendment, we are sending a signal that we are serious about stopping the flow of illegal immigrants over the border," Sessions said.
"A border fence, combined with National Guard forces, increased border patrol agents and more bed space for arrested illegal aliens, will help us reach a tipping point where the scales tip from illegality to legality.
"If we continue to send signals like this, that the open-border days are over, people will know that it makes more sense to apply and come into our country legally, according to our laws, rather than trying to come in illegally."
The amendment represented a rare victory by the Senate's most conservative members in the fight over what to do about massive illegal immigration into the country, most of it over the porous 13,162 kilometre US-Mexico border.
Currently there are an estimated 11.5 million undocumented immigrants in the country, and various proposals on how to address the problem are under consideration, including a guest-worker program backed by President George W. Bush, and a tough House of Representatives draft law which would criminalise illegal immigrants.
The House's bill provides for building a border wall, almost twice as long as the Senate's fence plan at about 1,000 kilometres.