The Kerry Stokes-led media group, that includes TV broadcaster Seven Network and The West Australian newspaper, on Thursday announced chief financial officer Jeff Howard will take over the role.
"Jeff has an immense depth of experience and exposure across the broad media industry and the right balance of skills to deal with a dynamic and evolving media landscape," Mr Stokes said.
"Having worked as SWM's chief financial officer since January 2020, he is well positioned to continue the momentum created by James.
"His commercial knowledge, passion and commitment will ensure a strong performance focus at this critical time of change and innovation for the industry."
Mr Warburton gave no indication of the reasons behind the unexpected move and promised a seamless transition to Mr Howard, an "extremely talented leader".
"It has been an incredible journey at SWM and with an exceptionally talented team in place, the time is right for the company to take the next step," he said.
"I take great pride in the transformation of SWM in recent years and its position as the leader in total TV in both ratings and revenue."
Mr Warburton has overseen an eventful period for Seven West, in which the company secured long-term cricket and AFL broadcast deals and the acquisition of regional TV network Prime in 2021.
But the group has faced falling revenues amid a structural decline across the media industry, and the fallout from Ben Roberts-Smith's defamation case loss.
Mr Roberts-Smith, a former soldier whose legal fees were bankrolled by Mr Stokes, resigned from his role as general manager of Seven Queensland in June.
Mr Howard said Mr Warburton leaves the company in a strong position to take advantage of the opportunities ahead in an ever-changing industry.
Seven West says it has commenced a search for a new chief financial officer.
Shares in the company dropped two per cent to 24.5c shortly after the ASX opened on Thursday.
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