Mr Briggs stepped down as Minister for Cities and Built Environment in the Turnbull government after the public servant raised concerns about his behaviour following dinner and drinks with Mr Briggs and his chief of staff during an overseas trip.
'Nothing illegal has been alleged or in fact did occur,' he told reporters in Adelaide.
The incident occurred during an official visit to Hong Kong.
He said the public servant went home after the gathering and made a complaint in the days following.
'I've apologised directly to her but after careful reflection about the concerns she raised and the fact that I was at a bar late at night while on an overseas visit, I have concluded this behaviour has not met the particularly high standards for ministers.'
Mr Briggs said the woman was offended but stopped short of revealing details of what took place.
He said he discussed the matter with Prime Minister Malcolm Turnbull, and they both agreed he should step down.
'He was of the view this did not meet what he expects of his ministers' behavioural standards in respect of the code of conduct,' Mr Briggs said.
'I accepted that and therefore took that action.'
Mr Briggs confirmed he plans to stay on as member for the seat of Mayo in South Australia.
The 38-year-old has served in federal parliament since 2008.
