Collins has become a founding partner at the Mayfair-based firm.
Montfort was founded by Nick Miles and Hugh Morrison, who launched M:Communications in 2002, growing it to become one of the City’s top PR firms with revenues of £14m.
The new venture came to light when Montfort and Morrison’s names appeared on the ‘Intention To Float’ document filed by luxury shoe company Jimmy Choo last September. The agency currently employs about a dozen members of staff.
Collins has known Miles and Morrison for several years. She previously discussed a merger between M:Communications and Penrose, the consultancy she founded in 1998 that in 2010 became part of the new agency MHP.
PRWeek revealed last year that Collins is to leave her role at MHP, saying that she decided to take a "step back" given her other commitments. Collins is also a founder steering committee member of the 30% Club, which aims to increase representation of women on UK boards, and a non-executive director of JP Morgan Overseas Investment Trust.