Lady Hermon has confirmed she is standing down and will not run to retain the Westminster seat she has held for 18 years.
She first won the North Down seat in 2001 as an Ulster Unionist.
She left the party in 2010 after it agreed an electoral pact with the Conservatives and since then has sat as an independent unionist.
In a statement she said it had been a “particularly difficult” decision – but the right one for her family.
The 64-year-old said she was “profoundly grateful” to all those who had voted for her in the last five general elections, adding it was with “enormous sadness” that she would not be standing in the general election on 12 December.
“Now, however, my priorities for the next few years are to spend my time at home in Northern Ireland to see more of my family and to step back from the frontline of public life,” she said.
“If my successor enjoys the role of MP for North Down half as much as I have done, a smile will constantly be on his or her face.”
She entered politics in 1998, joining the Ulster Unionist Party having been impressed with its role in the Good Friday Agreement negotiations.
She lectured in law at Queen’s University Belfast at the same time as David Trimble, who went on to become leader of the Ulster Unionist Party (UUP).
Within the UUP, Lady Hermon was regarded as being on the more socially liberal wing of the party.
In July 2019, she voted in favour of legislation in the Commons to legalise same-sex marriage and decriminalise abortion in Northern Ireland.
In 2001, she won the North Down seat for the UUP, defeating the incumbent by more than 7,000 votes.
During the campaign she won the support of the Alliance Party, which withdrew its own candidate.
In 2005, she was the only Ulster Unionist MP to retain her seat after the party suffered a slew of defeats in the Westminster election.
Five years later, she formally cut ties with the party after it agreed an electoral pact with the Conservatives.
She then opted to sit in Westminster as an independent unionist MP.
She backed remain in the 2016 EU referendum and voted against Prime Minister Boris Johnson’s Brexit deal.