The brief is focused on providing senior-level advice to the retailer with "creative political engagement plans" in light of a new Parliament following the general election.
Pagefield will also provide counsel and support to Asda on political issues and audience management, working closely with its in-house public affairs team.
Asda is the third largest UK supermarket in terms of market share, employing over 140,000 people and serving more than 19 million customers a week. Last year, competition authorities blocked a proposed merger between Asda and the second-biggest supermarket, Sainsbury's.
Asda's senior director of public affairs, Chris Lowe, said: "We are pleased to begin work with Pagefield at this critical time for the business. With a new government, we will be working closely with Pagefield to access senior-level advice, creative political engagement, and day-to-day support."
Asda is the latest win for Pagefield after recently picking up peer-to-peer platform RateSetter, the UK's manufacturing trade body Make UK, and Britain's oldest working hospital, St Barts.
Pagefield chief executive Oliver Foster said: "We are thrilled to have won this brief as a new Parliament has been returned. Asda is a brilliant retailer that employs over 140,000 people in the UK and we look forward to working closely with the team in Leeds and London in support of their exciting campaigns across the UK."
In separate news, Pagefield's advisory board chair, Teresa Graham CBE, has been appointed Dame Commander of the Order of the British Empire (DBE) in the 2020 New Year’s Honours List, for services to small business.