It was a perfect landing for Williams and two astronauts, Flight Engineers Yuri Malenchenko and Aki Hoshide, as they touched down in the dark, chilly expanses of central Kazakhstan on board a Russian Soyuz capsule.
The three astronauts landed at 0726 IST in the town of Arkalyk.
Helicopters rushed with the search-and-recovery crew to assist them, as their capsule parachuted down some 35 kilometres from the planned touchdown site due to a procedural delay.
Another three astronauts remain on board the International Space Station (ISS) and will return next year.
Earlier, the trio bid farewell to their fellow astronauts at the ISS, Flight Engineers Kevin Ford, Evgeny Tarelkin and Oleg Novitskiy.
The trio undocked from the Rassvet module of the ISS yesterday.
The return of Williams, Hoshide and Malenchenko has wrapped up a 127-day space journey for them, since their launch from the Baikonur Cosmodrome in Kazakhstan on July 15, this year, including 125 days spent aboard the ISS.
Williams, 47, now has spent a total of 322 days in space during her two long-duration missions. She previously served aboard the ISS as an Expedition 14/15 flight engineer from December 9, 2006, to June 22, 2007.
Williams now also holds the record for spacewalking time for female astronauts.
Williams has a total of 50 hours and 40 minutes of spacewalking time over seven spacewalks, including the three she conducted during Expeditions 32 and 33.
This was the second trip into space for Hoshide of the Japan Aerospace Exploration Agency, who visited the station as an STS-124 mission specialist aboard space shuttle Discovery in 2008.
Russian Soyuz Commander Malenchenko wrapped up his fifth spaceflight for a total of 642 days in space, placing him seventh on the all-time endurance list.
NASA TV will air its post-landing video file, including interviews with the crew, later.
The undocking signals the end of Expedition 33 and the start of Expedition 34 under the command of Ford, who will remain on the station with Novitskiy and Tarelkin until March.
Williams transferred the helm of the orbiting laboratory to Ford during a change of command ceremony on Saturday.
Three additional Expedition 34 flight engineers – NASA astronaut Tom Marshburn, Canadian Space Agency astronaut Chris Hadfield, and Russian Federal Space Agency cosmonaut Roman Romanenko -- are scheduled to launch from Baikonur on December 19 and dock to the station two days later for a five-month stay.
Hadfield will become the first Canadian to command the station when Ford, Novitskiy and Tarelkin depart, marking the start of Expedition 35.
The Soyuz remains the only means for international astronauts to reach the orbiting laboratory since the decommissioning of the US shuttle fleet in 2011.