The flight attendants faced furloughs because of United's massive merger with Continental Airlines. The flight attendant union represents about 25,000 workers.
"Through collaborative efforts, AFA was able to engage management in meaningful discussions on how to ensure that no flight attendant is forced out on the street without a paycheck," said Veda Shook, AFA international president.
United, which was formed by a merger of UAL and Continental in 2010, has been working to win back customers who turned to rivals after the airline faced severe service-related and operational problems in 2012.
"We are pleased we came to an agreement that will benefit our flight attendants," United spokeswoman Megan McCarthy said Thursday in an email to CNBC.
Last month, United told CNBC it offered opportunities to flight attendants for both voluntary furloughs and job-sharing programs to try to avoid having ground them involuntarily, but the programs failed to generate enough volunteers.
"This new agreement enhances the original bridge agreement with seniority protections and benefits that would otherwise have not been possible without our mutual effort," said Marcus Valentino, AFA president who represented Continental before the merger.
—By CNBC's Karma Allen. Follow him on Twitter