Ashworth will join the drinks industry’s voluntary marketing regulator on October 24.
He is currently working at the Cabinet Office’s behavioural insights team, leading health policy.
Ashworth will join Portman as it launches a consultation on a review of its code of practice on marketing and packaging of alcohol drinks.
Ashworth said: “The Portman Group is already a highly-respected alcohol regulator and is a key player in challenging the industry to address the adverse aspects of our drinking culture.
“I firmly believe that self-regulation based on a tough code of practice that is rigorously monitored and enforced is the right way forward.”
Ashworth replaces David Poley who is leaving the drinks industry.