Opposition home affairs spokesman Jonathon Duniam will not seek re-election for his Tasmanian Senate seat and will leave parliament before the end of 2026.
His decision came as a poll published by Nine newspapers put primary support for One Nation ahead of Labor and showed support for the coalition sinking further.
The latest Resolve Political Monitor put support for Pauline Hanson's party at 29 per cent, with the ALP on 28 per cent and the coalition a distant third on 20 per cent.
It also found Senator Hanson had surged past Anthony Albanese as preferred prime minister with 33 per cent support compared to 29 per cent, with Liberal leader Angus Taylor on 16 per cent.
Earlier, Senator Duniam said he wanted to step back from politics after 10 years in federal parliament to spend more time with his family, including his three children.
"Ten years, on top of 15 years prior to that of being in and around politics, 25 years of my life dedicated to long hours and being away from home a lot has taken a toll on my family," the 43-yeear-old told reporters in Hobart on Sunday.
"This job has been a very serious one, and as a result, has taken up a lot of time and a lot of energy.
"It is odd to fight hard to get in. It's even odder when you fight harder to stay and then to pull up stumps.
"When family come into it, you can't think twice about it. Your priorities become very, very clear."
The loss of Senator Duniam was another blow for the Liberal Party, Home Affairs Minister Tony Burke said.
"The Liberal Party lose one of their best and brightest when he leaves the parliament," he told Sky News on Sunday.
Senator Duniam said poll numbers had not influenced his decision to retire, despite a surge in One Nation's primary vote placing the party ahead of Labor and the coalition.
"This is something that we've been weighing up, and my team, my colleagues in Canberra, trusted friends know that I've been weighing this up for a while," he said.
"A good friend of mine told me graveyards are full of indispensable people and at the end of the day, someone else is going to take my place."
Senator Duniam first entered federal politics at the 2016 election, when he became the only new Tasmanian member of the upper house.
He came to Canberra after previously serving as an adviser to former Tasmanian Liberal senator Eric Abetz, and later as a deputy chief of staff to Tasmanian premier Will Hodgman.
He served as an assistant minister for forestry and fisheries in Scott Morrison's government and later held the opposition spokesman role for the portfolio following the Liberals' 2022 election defeat.
Senator Duniam became the opposition home affairs spokesman after Angus Taylor took over as opposition leader in February.
He said his long lead time for his retirement would allow a successor to build up a profile before the next election, which must be held before May 2028.
"I discussed my decision with Angus some time ago and he has asked me to continue for a short period of time to complete work on our immigration policies," he said.
"Now is the right time for my party to choose new Senate team members who will carry forward the fight for Tasmania and for the values in which the Liberal Party believes."
Fellow Tasmanian Liberal Wendy Askew announced her retirement earlier in June, with political operative Brad Stansfield saying he would stand for pre-selection.
