The AA's media account was previously split between Zenith Media, which held the membership and insurance business, and Manning Gottlieb, which had the AA Car Loans account.
Manning Gottlieb was appointed after a pitch against Zenith and Carat.
The move follows a creative review by the AA last year that resulted in the appointment of M&C Saatchi. The agency has gone on to create the "Just Aask" campaign.
The AA's above-the-line spend in the past year was £19 million. However, together with below-the-line activity, it is expected to spend £34 million in the year ahead.
Manning Gottlieb has hired Jeremy Tester, the former managing director of ADazzle and PHD client services director, to head the AA account team.
It also works for the sister Centrica brand Goldfish.
Clare Salmon, the AA's director of marketing and sales, said: "We were very impressed with the way Manning Gottlieb OMD responded to the brief and feel that it understood the direction and vision the AA wants to pursue. This is the first time the AA's account has been consolidated through one media agency and is in line with the AA's truly integrated approach announced this year."
M&C Saatchi launched the AA's "Just Aask" strategy in May to replace the previous "The fourth emergency service" positioning developed by HHCL & Partners. The AA also retains Rapier and EHS Brann to work on its below-the-line activity.