Fair Work Commission vice-president Michael Lawler has resigned on the eve of his deadline to respond to a report on his controversial use of paid sick leave.

Mr Lawler has been embroiled in controversy for taking paid sick leave from his $435,000-a-year job while helping his partner - disgraced ex-union leader Kathy Jackson - defend a lawsuit over large-scale theft from the Health Services Union.

His resignation on Thursday came a day before he was due to respond to the report.

The report, by barrister and former judge Peter Heerey, was the result of a four-month investigation.