Shouesmith officially took up her role this month, after a short stint at fellow IPG-owned agency McCann Worldgroup.
She will work underneath head of public affairs Joey Jones, a longtime Sky News journalist and briefly an adviser to Theresa May, who joined Weber in September 2016.
Public affairs at Weber is overseen by Jon McLeod, chair of corporate, financial and public affairs, UK. McLeod is a Labour Party member.
Previously a Conservative Campaign Headquarters staffer, Shouesmith joined Number 10 in 2011. Over the next five years she held a number of roles including private secretary to chief of staff Ed Llewellyn, special adviser to Samantha Cameron and, in the run-up to the 2015 general election, political operations manager.
She worked at Stronger In during last year's EU referendum, in an external relations role. Her job was to persuade celebrities and corporates, from Alexa Chung to easyJet, to back a 'remain' vote.
After Cameron left Downing Street she joined ad agency McCann, working in the office of UK CEO Mark Lund.
The Office of the Registrar of Consultant Lobbyists lists De La Rue, Tregarth and Volvo Bus Corporation as clients of Weber Shandwick UK.