The controversial $8-billion US pipeline, tied up in the approval process for six years, would transport up to 830,000 barrels of oilsands crude per day from Alberta to the U.S. Gulf Coast.
If approved as expected in the Republican-led Senate next week, the issue could then go straight to the Oval Office.
Congressional approval would put President Barack Obama in a political bind just days after he concluded a surprise deal with China to limit greenhouse gas emissions.
The president, who has the power to approve or veto the bill, is believed to view an attack on global warming as a potentially significant part of his legacy as the country's 44th president. He has two years remaining in office.
Environmentalists have seized on the Canadian pipeline as a symbol of corporate North America's failure to help save the planet from the effects of global warming.
Republicans, victorious in the Nov. 4 congressional elections, where they campaigned heavily on the need for Keystone, have been pushing for approval of the project amid objections from some Democrats.
Keystone key to energy independency: senator
Still, Democrats from oil-industry-dependent states such as Louisiana support the project.
"It is time for America to become energy independent, and that is impossible without the Keystone pipeline and other pipelines like it," Democratic Senator Mary Landrieu of Louisiana told reporters Wednesday.
She and Senator John Hoeven, a Republican from North Dakota, introduced the bill on May 1.
Landrieu, who chairs the Senate energy and natural resources committee, is fighting for her political life as she faces a run-off race Dec. 6 that will determine whether she can serve another six-year Senate term beginning in January.
Landrieu acknowledged to reporters that she had no commitment from Obama that he would sign a Keystone bill if Congress sends one to him.
As it stands, the bill would accept a U.S. environmental impact study issued by the secretary of state in January, saying it "shall be considered to fully satisfy" other pending environmental and endangered species reviews.
As well, the bill mandates that any appeal against permit requirements must be expedited straight to the U.S. Court of Appeals.
There had been reports Wednesday that the House vote might take place today.