A former commercial director of FT.com, Payne was promoted to UK ad director last June when her predecessor, David Walsh, moved over to a short-lived role as the worldwide ad director.
Payne, 34, has worked at the FT for five years. She becomes the third high-profile departure from the troubled paper in as many months.
In March, Walsh left following a restructure of the company's ad department that saw his worldwide position scrapped. He was followed just weeks later by the FT's marketing director, Tim Ward, who had just overseen the launch of a £3 million ad campaign to support an overhaul of the paper.
The FT had a miserable first few months of the year with ad revenues down 18 per cent compared with the same period last year. This prompted Pearson, which owns the FT, to warn that the advertising outlook for the rest of the year looked uncertain.
The title's circulation has also suffered - in April it stood at 445,349, down nearly 5 per cent on the same month in 2002 once free bulk giveaways are taken out of the equation.
No-one at the FT or Loot was available for comment.