Ben Nelson forced a concession in the phrasing about abortion funding
Democrats in the US Senate say they have secured the vote of a key holdout senator and will now have the 60 needed to pass sweeping healthcare reforms.
Senator Ben Nelson had been concerned that federal money would be used to fund abortions.
But after a day of talks on Friday Democrats said they had agreed phrasing that would secure his vote.
President Barack Obama described the compromise as "a major step forward for the American people".
"After a nearly century-long struggle we are on the cusp of making healthcare reform a reality in the United States of America," Mr Obama added.
If the Senate passes its version, it must be reconciled with a House version before it can become law.
Democratic Senator Charles Schumer said there had been 13 hours of talks on Friday but that Sen Nelson was now "in agreement".
Sixty votes are needed to bypass a lengthy debate, or filibuster, in the Senate.
Votes could begin in the Senate in the early hours of Monday with final passage possible by Christmas Eve.
President Obama has set the issue as a key plank of his first term and wants the Senate to pass the bill by year's end.
Republicans fiercely oppose the reforms and have tried to delay passage as long as possible.
In his weekend address, Mr Obama said: "Now - for the first time - there is a clear majority in the Senate that's willing to stand up to the insurance lobby and embrace lasting health insurance reforms that have eluded us for generations."
The legislation - designed to secure coverage for millions of uninsured Americans - could lead to the biggest changes in US healthcare in decades, if approved.
Under the Senate bill, most Americans would have to have health insurance, while private insurers would be banned from refusing to provide insurance because applicants had pre-existing medical conditions.
Insurance would be made more affordable with subsidies available to help those in lower income bands, the Democrats say.
People would also be able to take part in new insurance market places and be able to choose to buy government-sold insurance from 2014, a provision intended to help regulate the prices charged by private companies.
Large companies would be required by law to provide coverage to staff. The costs would be covered by government cuts on future Medicare spending.