Nolan's promotion comes just months after In Style was moved into UK-based IPC Media, which was acquired by Time-owner AOL Time Warner last summer.
Deputy editor Louise Chunn will take over from Nolan while a replacement editor is found.
News of Nolan's departure was accompanied by the news that IPC Southbank, the division that houses In Style, has appointed Walsh Trott Chick Smith to create an above-the-line integrated marketing campaign for the fashion title, a year after the magazine debuted in the UK.
The UK edition of In Style has struggled to compete in an already crowded women's market, despite its success in the US where it is among the top women's lifestyle magazines.
Walsh Trott already handles the above-the-line work for IPC's TX division and beat IPC roster agencies Roose, Cartwright and Farm to win the work.
Media planning and buying is held by IPC Southbank's incumbent MediaCom.
Helen Farquhar, marketing director of IPC Southbank, said: "Walsh Trott jumped at the brief to deliver a completely new creative design to drive trial and awareness among In Style's core audience group.
"Its strong strategic grasp of the market and the brand enabled it to produce a very distinctive campaign that will have great stand-out in the marketplace."
Meanwhile, In Style publisher Katy Egan has been promoted to the position of business development manager for Southbank's portfolio of magazines including flagship women's glossy Marie Claire. Egan will report directly to Southbank managing director Tim Brooks.
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