Grove based team said it has appointed Dave Robson to work with Felipe Massa in 2015.
Jenson Button's race engineer at McLaren is moving to Williams.
In a media statement on Monday, the Grove based team said it has appointed Dave Robson - who since 2010 has been Button's race engineer - to work with Felipe Massa in 2015.
Massa's existing engineer, Andrew Murdoch, has been promoted to senior performance engineer, "with a focus on Valtteri Bottas' car" at the races, Williams added.
Bottas' race engineer Jonathan Eddolls retains his role.
"Off the back of a great 2014 campaign Williams is determined to continue this positive momentum into the new season," said technical boss Pat Symonds.
Meanwhile, following reports McLaren is set to drop its silver livery for 2015 and switch to Honda white, a team spokesman said: "McLaren-Honda has not yet finalised its livery for 2015 and beyond."