Leslie, who was appointed to head the South African fine paper group in 2003, will be replaced in the short term by his predecessor chairman Eugene van As, while a successor is sought.
The resignation follows a period of poor results for the group, and comes as the firm warned that second-quarter earnings will deteriorate as result of the current global paper market conditions.
Shares in Sappi fell 2.2% on the news to 7.37 (SAR80.5).
The announcement was made at Sappi's annual general meeting, where the company admitted that price increases announced in Europe last year had failed to be accepted. It added that despite positive demand for its products, results had continued to disappoint.
The firm cited the supply/demand balance and the increasing rise in input costs as the main problem areas.
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