Barrington-Wells, who joined Dragon earlier this month, will head up the luxury brands and lifestyle division.
He was previously at Langham Hospitality Group for seven years as its director of public relations and director of marketing partnerships.
Before that, Barrington-Wells was a consultant at Chime Communications where his clients included Berkeley Homes.
He said: "The opportunity to move to Dragon Associates at this extremely exciting time for the company, with our business growing rapidly, was simply too good to turn down."
Rumbellow, meanwhile, will represent its clients across the financial services, luxury and lifestyle sectors.
She was previously part of the in-house comms teams for the insurance broker Willis Group and, before that, for the mining giant Anglo-American.
Rumbellow’s expertise includes media relations, issues management and internal comms.