Southern Cross confirmed Jackson's departure today. Jackson could not be reached for comment.
Jackson joined in September 2015, overseeing a period in which Southern Cross received its peer-to-peer license.
Jackson's has left to pursue another role and will be replaced in the interim by Terry Butler, a Southern Cross director who becomes Acting CEO.
During Jackson's leadership, Southern Cross made the move to become a peer-to-peer lender to take business from the big banks. According to its recent figures, Southern Cross loans under arrangement grew by 24.8% in the year to September, with investor funds up 19.9%.
It is unclear whether Jackson is staying in the finance sector. Prior to joining Southern Cross, Jackson worked as a commercial manager for BNZ, ASB, Look Finance, and the National Bank of New Zealand.