Hulkenberg impressed in 2010 but will not keep his seat alongside Barrichello
Brazilian veteran Rubens Barrichello will stay at Williams for a second season in 2011 but the team have decided to drop rookie Nico Hulkenberg.
Barrichello is expected to be joined in 2011 by the Venezuelan Pastor Maldonado, who won the GP2 feeder series at the fourth attempt in 2010.
Team owner Frank Williams said Barrichello, 38, had brought "technical expertise, experience and passion".
He added: "He has delivered everything we could have hoped for this season."
Williams paid tribute to Hulkenberg's efforts, saying: "At Williams we have for many years tried to bring new talent into the sport, and we are convinced that Nico will go on to great things.
Hulkenberg 'amazed' to take pole
"We wish him well and hope that our paths will cross again in the future."
After a shaky start, the 23-year-old German had an increasingly impressive debut season in F1.
The highlight was a superb pole position in drying conditions at the Brazilian Grand Prix, where he beat the new world champion Sebastian Vettel by more than a second.
It was the first pole position for five years for a team that dominated F1 for much of the 1980s and 1990s, but whose 113th and last win came thanks to Colombian Juan Pablo Montoya at the 2004 Brazilian Grand Prix, the final race of that season.
Williams finished sixth in the constructors' championship in 2010, with their best result a fourth place for Barrichello in the European Grand Prix in Valencia in June.
Williams have replaced Hulkenberg because they need finance to replace the loss of three major sponsors at the end of the 2010 season, which finished in Abu Dhabi on Sunday, and Maldonado comes with substantial backing from companies in his home nation.
Hulkenberg said on his website: "I heavily regret that (I am leaving), because I would have been happy to stay with Williams.
"I want to thank the team for a great time and I wish Williams all the best for the future."
His manager Willi Weber added: "I am negotiating with other teams. Nico will have his seat in F1 in 2011."
A Williams statement said their second driver would be confirmed "before the end of the year".
The Venezuelan, who has not yet been confirmed by Williams, will drive for the team at the post-season tyre test in Abu Dhabi at the end of this week.
Barrichello, who has driven in more grands prix than anyone in history, will be entering his 19th season in F1 in 2011.
The season-opening race in Bahrain will be the 306th race, and 302nd start, for the former Jordan, Stewart, Ferrari, Honda and Brawn driver.
Hulkenberg's pole lap in Brazil