The outgoing boss of the Turnbull government's controversial construction industry watchdog says he has no regrets about his sometimes turbulent career.

In a letter to colleagues on his final day as head of the Australian Building and Construction Commission, Nigel Hadgkiss also anointed his preferred replacement.

Australian Building and Construction Commission boss Nigel Hadgkiss resigned earlier this month. Credit:Simon Schluter

Hadgkiss resigned from his $426,000 job earlier this month after admitting to breaching workplace laws during his earlier tenure as head of the Fair Work Commission's building industry office. After a two-week transition he officially left the job on Wednesday.

"It brings to an end a 48-year career in law enforcement. In no way do I regret any of that time, challenging though much of that journey has been," he said in the internal memo.