Simon Davies, the advertising sales director at Ireland on Sunday, takes over from Dear, who has already left Associated.
Dear was made the ad director at The Mail on Sunday in 2000, replacing Sally de la Bedoyere, who was promoted to managing director at the Evening Standard. De la Bedoyere left Associated last year following the appointment of Mike Anderson as its managing director.
Davies has previously had spells in sales roles at The Mail on Sunday, the Daily Express and The Scotsman. His team at The Mail on Sunday includes Rob Atkinson, the head of trading, and the sales controller, Steve Atkinson.
The changes were instigated by Mike Ironside, the managing director of The Mail on Sunday.
Last month, the Daily Mail & General Trust, the owner of Associated, warned that its advertising revenues were likely to be flat for the remainder of the year. It said that national titles had recovered from the slowdown surrounding the Iraq war but that there were no signs of a real upturn.
Associated reported flat income of £419 million for the six months to March 2003.
Advertising revenues were up 0.4 per cent at Associated during the six-month period but felt a sharp drop of 12 per cent during March.
The most recent ABC figures, published last week, show The Mail on Sunday down 1.9 per cent to 2,330,043. Ironside was unavailable for comment.