The British racer had previously held the title of development driver, a role which culminated in her becoming the first female driver to drive in a Grand Prix event for two decades when she took part in FP1 in Britain and Germany.
In her expanded new role Wolff, 31, will drive the Mercedes-powered FW37 in two FP1 sessions during 2015, as well as at two test days. She will also conduct extensive simulator testing to help aid development of the Williams’ 2015 and 2016 challengers.
Speaking about her new role Wolff said: “This is another step in the right direction for me. I am delighted Williams are recognising my progression, hard work and that it is performance that counts.
“Williams is at a very exciting stage in its history and we are moving into 2015 with fantastic momentum, I’m proud to be part of the team. I’ll be using my position to work closely with Felipe (Massa) and Valtteri (Bottas) to make sure that the FW37 builds on the strong performance shown by the FW36.”
Williams’ deputy team principal Claire Williams added: “We are delighted to have Susie continuing with the team next season in this new role. She continues to impress us with her strong technical knowledge, the feedback she delivers and the performance when she drives the car both on the track and in the simulator.
“She has steadily increased her time behind the wheel since she joined us in April 2012 and her appointment as official test driver was a natural progression. We have a very strong and stable driver line-up for 2015 and this will be a key asset as we look to build on a positive 2014 season.”