The agency was given the nod after contesting the business with Mitchell & Partners and Universal McCann.
The account is the largest in the state and the eighth-largest in Australia.
MediaCom has held the account, which is subject to statutory review, for the past four years.
Nicole Boyd, the MediaCom Brisbane managing director, denied the agency had significantly lowered its fee to keep the business.
"The fee is always a consideration, but the government's not just looking for that," she said.