His promotion coincides with the departure of Michael Pring, Dare's managing partner, who has resigned less than a year after the merger with MCBD.
Pring had been in discussions with Gregor Angus, the president of Dare's parent company, EDC, about a wider group role but decided to leave for "fresh challenges".
Pring said: "I've had a fantastic innings at MCBD and, more recently, Dare, but now is the right time to make a change."
Horry, who joined Dare as a board planner from Abbott Mead Vickers BBDO in 2006, was promoted to the role of joint planning director the following year and has been leading Dare's new-business efforts since the merger with MCBD.
In his new role, Horry will report to the chief executive, Lee Leggett; they will work closely with John Owen, the deputy chairman, on the day-to-day running of the agency. Helen Calcraft remains the agency's chairman.
Leggett said: "Toby's background and experience make him the ideal man for the job. He's a genuine all-rounder who I know will bring enormous energy to the role."
Pring joined MCBD from D'Arcy in 2001, was promoted to the agency's board in 2002, to new-business director in 2003 and to joint managing director in 2007.