LONDON—Steffan Williams is departing Capital MSL, the City PR firm he co-founded in 2001.

Williams, who has helped oversee Capital's growth in the UK and abroad over the past 12 years, is to take on a senior role at rival financial agency RLM Finsbury.

Co-founder Richard Campbell remains at Capital MSL as chief executive, according to a statement from parent agency MSLGroup.

"We wish [Williams] well and thank him for his twelve years at Capital MSL and within the MSLGroup," said an MSLGroup spokesperson. "Co-founder Richard Campbell continues in his role as chief executive of the firm, supported by a strong and broad management team, who have successfully presided over industry leading growth in recent years."

Prior to launching Capital MSL in conjunction with Publicis Groupe, Williams worked at Thomson Reuters and Citigate, after leaving a career in investment banking.

Capital's growth in recent years has been underpinned by its international presence, which includes a substantial Middle East operation, along with partnerships with MSLGroup's other corporate and financial firms, including JKL, CNC and Kekst.