Hilton (pictured) - who has worked at Golin for 13 years, including five years as MD at the London office - takes the role of global engagement director for Unilever at Interpublic Group.
She will join the Unilever IPG leadership team and continue to lead Golin’s Unilever assignments globally, Golin said.
Hilton, the current president of Women in PR, will transition to the new role in 2020 and remain based at Golin’s London office.
Golin said it's in the process of appointing a new London MD.
Jon Hughes, Golin global co-CEO, who returned to the UK from Hong Kong in 2018 to oversee the EMEA and Asia businesses, said: "I hired Bibi in 2006 and have had the pleasure of working with her for 13 years. Under her leadership, our London office has become one of the most progressive and creative agencies in the UK, winning agency of the year seven times in five years and launching industry-leading initiatives including Golin B&B.
"As anyone who knows her will testify, Bibi loves working closely with clients to help solve their business challenges and develop impactful creative work and I know she will thrive in this exciting new role."
Meanwhile, Golin said Luscombe - who joined almost two years ago from Bell Pottinger, where she ran the collapsed company's 80-strong Engage division - is leaving to "take up a new opportunity in the corporate and b2b sector in the New Year". Luscombe declined to reveal details of her new agency role.
Her position at Golin has included overseeing the corporate, b2b and tech businesses.
Hughes said: "I want to thank Emily for her contribution to the agency and her stewardship of some of our largest and most important clients. Naturally, we wish her all the very best for the future."
Golin, a double winner at the PRWeek Awards in 2019, was the UK's 16th biggest PR agency in 2016, with estimated revenue of £27.5m, up six per cent on the year. Headcount was around 260, according to the PRWeek UK Top 150 Consultanices report.