Ms Williams will be travelling into space for the third time.
The Boeing Starliner, which is set to take Indian-origin astronaut Sunita Williams to space for a third time, will lift off from the Kennedy Space Centre in Florida around 10 pm today.
An earlier attempt on May 7 had been postponed hours before lift-off due to a technical glitch.
US space agency NASA (National Aeronautics and Space Administration) said that, if all goes well, the Starliner will dock to the forward-facing port of the International Space Station's Harmony module and Ms Williams and Butch Wilmore, her co-passenger, will remain at the station for about a week to test the Starliner spacecraft and its subsystems.
After that, NASA will work to complete final certification of the transportation system for rotational missions to the orbiting laboratory as part of the agency's Commercial Crew Program.
Ms Williams, the poster girl for women aspiring to fly into space, will be travelling into space for the third time and could make history as the first woman to fly on a maiden crewed mission of a new space shuttle.
She has spent 322 days in space and also held the record for the maximum hours of spacewalks by a woman, before being overtaken by Peggy Whitson.
The astronaut went on her first space voyage on December 9, 2006, which lasted until June 22 the next year. During that time, she established the record by going on four spacewalks that added up to 29 hours and 17 minutes.
The 59-year-old had admitted to being a bit nervous about the mission but said she had no jitters about flying in a new spacecraft. She had helped design the Starliner, working with engineers from NASA and Boeing. "When I reach the International Space Station, it will be like going back home," she said.
The nearly 10-day mission will help the Starliner prove its space-worthiness. It would also prove the team's readiness to achieve NASA certification and fly long-duration missions for the US space agency.
In a statement about the previous launch being cancelled, NASA said, "Boeing, United Launch Alliance and NASA scrubbed the previous launch opportunity on May 7 due to a suspect oxygen relief valve on the Atlas V rocket's Centaur second stage. Since, teams have removed and replaced the valve, and completed an assessment of the Starliner's performance and redundancy after discovering a small helium leak in the spacecraft's service module."