Carter, who emerged from five internal candidates, has been handed the role of display advertising director within Mirror Group Newspapers. He will report to the ad director, Neil Hurman.
However, with Hurman set to take a commercial director role and act as Apollo's client at Trinity Mirror should the joint sales house go ahead, Carter will effectively lead the Mirror half of the advertising sales operation.
"I have been given an opportunity to drive the MGN display department forward and to play a major part in a ground-breaking new venture," Carter said.
The appointment of a director for The Mirror's ad team has been eagerly awaited since plans for the Telegraph Group-owned Apollo were announced in March.
The appointment of a Mirror ad director acceptable to all has been seen as a crucial step in putting the joint sales house together. The delay in the announcement had fuelled speculation that the deal may have been in difficulty.
Carter's appointment will remove some of these concerns, but other issues, such as pensions and the integration of IT systems, are understood to be still under discussion.
Carter joined Mirror Group as the head of client services, as part of the restructuring of ad sales, which was introduced by Hurman in December 2000. Carter had worked as a group head for The Sun and sponsorship sales manager for Times Newspapers, before moving to Attic Futura in the summer of 2000.
"Out of a first-rate field of internal candidates, Dominic's vision for our future and his credentials to deliver it emerged the strongest," Hurman said. "I'm delighted that he will now be able to play a more prominent role in shaping our futures."