The agency has also poached Starcom Mediavest's TV buying director, Kevin West, who will now head up the COI TV account, which Carat won from Starcom last month.
Head of media Mark Jarvis remains in his position, but as exclusively revealed in Media Week, he is stepping away from the day-to-day running of the media department and will be more involved in the running of the business alongside managing director Neil Jones.
Jarvis will still be chief negotiator for the business, with Hobbs looking after the implementation of those deals and reporting directly to Jones.
Hobbs, who has been with Carat for 10 years, said: "Mark will be taking care of face-to-face negotiations with media owners and I will be focusing on how we use that value."
In the other major change at the agency, Carat brought in West from Starcom Mediavest, after persuading him to follow the £77.6m COI TV account.
West has had a 12-year relationship with COI and the Government's communications arm indicated to Carat that it would like West to stay with the account.
Jones said: "COI were very clear to us that he knew the business better than anybody else. It was logical that we spoke to him. "Due to the inclusion of the Department of Transport in the recent COI pitch, West said it was a "good opportunity to expand my role with a new challenge, but with safety in the back pocket."
Jones said that the movement of West from Starcom was not a deal breaker when it came to the pitch, but he has no problem searching out talent when a client requests it.
He said: "I went down there and they said ‘what's your view of Kevin West, would you like to interview him?' and I said ‘yes'.
But it was nothing to do with winning or losing the business."
The Carat MD added that he had no problem with people following accounts "as long as they are open to change and adaptable".
Despite the best efforts of Starcom to keep West at the agency, he decided to follow the account he has a long-term relationship with.
"They did try to keep me and they offered me different jobs," he said. "It was a difficult decision, but I wanted to stay with the heartland I know."
West will also have responsibility at Carat for interactive TV, a technology the COI has already made extensive use of.
It made 32 interactive deals with Starcom last year.
Carat's extension of Renault account
Carat has retained its £350m pan-European Renault planning and buying account.
The French car manufacturer has agreed a further three-year contract with the Aegis-owned media network.
Renault has been with Carat for more than three years and called for the review when senior members of the agency's French office departed, including president Henri Le Menestrel.
France constitutes Renault's biggest media spend with £160m, while in the UK the car manufacturer has annual billings of £60m.