He will be replaced by Kathy McAllister, former head of marketing at the BBC, who has been working at News Group Newspapers as a marketing consultant for the past month. It is not clear whether McCaskill has a job to go to.
McCaskill took the job as marketing director after Roland Agambar left to take up the post of chief marketing officer at rival publishing group Associated Newspapers.
He had worked at News Group for four years, having joined the company as head of marketing for Scotland and Ireland.
McCaskill worked from the organisation's Glasgow, Dublin and London offices. During his time at The Scottish Sun, it became Scotland's bestselling newspaper.
After working at the BBC, McAllister was director of marketing for youth organisation V, which aims to promote volunteering among 16- to 25-year-olds.
McCaskill's departure is the latest in a series of changes within the News International marketing team. In January, Jeremy Schwartz, former marketing director of Sainsbury's, was appointed to the new role of chief marketing officer.
According to the most recent ABCs The Sun has a circulation of 3.1m, while The News of The World reaches 3m readers.