Pagefield initially worked with the charity when it announced Ruth Hunt as its chief executive in July 2014.
The agency also supported the launch of the Workplace Equality Index and Stonewall’s annual awards, as well as its trans-equality campaign.
Pagefield will report to Rachel Cohen, director of comms at Stonewall. The brief is to provide ongoing strategic advice, comms support and assist the chief executive.
"Pagefield has assisted us with some vital projects in the past few months, which has helped us to communicate our work to a wide and varied audience," said Rachel Cohen, director of comms at Stonewall.
Oliver Foster, Pagefield’s managing partner, said: "Stonewall has really attained outstanding results in its 25 years of campaigning. It has been instrumental in achieving legislative equality for the gay and lesbian communities, and is working now to stamp out homophobia and to promote equality for LGBT people."