London - Former technical director Paddy Lowe is leaving Williams with immediate effect and has stepped down from the board of directors, the Formula One team said on Tuesday.
Lowe had been on an extended "leave of absence" since March 5, before the start of the season.
"After a period of careful reflection I have reached the decision that I will not return to work at Williams," he said in a team statement.
Lowe's position at the former world champions appeared shaky last year and worsened after the team failed to finish its new car in time for the start of testing in Barcelona and turned up two days late.
The team are last in the championship and has yet to score a point with a car that has been the slowest on track all season.
Williams finished last overall in 2018 and have not won a race since 2012.
Lowe joined Williams in 2017 from dominant champion Mercedes but last year's car - the first under his supervision - proved ill-handling and uncompetitive.
The family-owned British team have British rookie George Russell and Poland's Robert Kubica as their drivers.
"We understand and respect the decision Paddy has reached and wish him well for the future," said deputy principal Claire Williams.Reuters