Cullen, who had no previous experience in the financial services industry, is expected to remain with the company for the next few months. Prudential, who report on Wednesday, quickly reassured the sector that there was nothing amiss financially at the insurance giant.
The move marks the third recent departure of a senior executive from the company in the last two months. Chief executive Sir Peter Davis and Bob Head, finance director of Egg, the direct services arm of the Prudential, both announced that they were leaving last month.
Prudential shares fell 9p last week to 981p before rallying slightly this morning to 986p.
48-year-old Cullen joined Prudential in September from car retailer Inchcpae. It is expected that he will be paid compensation of about £350,000, his second large pay off in the last 12 months. Chief executive designate Jonathon Bloomer said the company had already appointed headhunters to help fill the post.