Last week the team announced Claire Williams would step down from her role as deputy team principal after the Monza race, with the Williams family leaving the team following the sale to American investment fund Dorilton Capital.
With a tight turnaround to the next F1 race, the Tuscan GP at Mugello, Williams has announced Roberts will become acting team principal starting from this weekend.
It remains unclear how long Roberts will hold the position, but the team has said he will keep the role "during this transitional period" following the overhaul of senior management personnel at Williams.
Roberts joined the team earlier this year as managing director of its F1 operations, having previously been McLaren's long-time operations chief. Roberts started his initial role at the beginning of June.
"I am delighted to be announced as Acting Team Principal for Williams during this transitional period," Roberts said.
"It is an exciting time ahead for the team, a new era for Williams and one that I am excited to be playing a part in. I look forward to the challenge ahead as we look to take the team back to the front of the grid."
Roberts' appointment is the latest change to the Williams senior management team since its takeover by Dorilton Capital, with outgoing Williams CEO Mike O'Driscoll announcing his intention to retire earlier today.
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Last week Williams announced a new board of directors, featuring Dorilton founders Matthew Savage and Darren Fultz, as well as former racing driver James Matthews.
For the first time in the team's history it will no longer be overseen by a member of the Williams family, following the departure of founder Sir Frank Williams and deputy team principal Claire Williams.
Claire Williams had been offered the chance to stay on at the team, but felt it was the "right choice" to leave during the transition period under the new ownership.