Penny Mordaunt, the Conservative representative for Portsmouth North, accepted the title at the seventh Pink News awards last night.
The prize was also shared by Jess Phillips, the Labour MP for Birmingham Yardley.
Until July 24, Ms Mordaunt served as the government’s minister for women and equalities, and defence secretary.
She took up the latter role for 85 days, starting in May this year, and is the first woman ever to have held the post.
During her 15-month spell as equalities minister she was a vocal advocate for the recognition of same-sex marriage in Northern Ireland.
On accepting the award, Ms Mordaunt said: ‘Thank you very much for the honour of this award and for the things we have got done.
‘You don’t achieve anything on your own in politics and we have got a few things done that I could not have done on my own.’
She added: ‘[Thank you to] all of those people who have supported, from every party and none, the actions taken over the last 12 months in particular.
‘In particular to all those campaign groups and individuals who fought so hard and tested the law and pushed government – together we did a huge amount, but there is still so much to do.
‘To do that well, we have got to reform and refresh our politics so that it’s effective and it’s actually responsive to the society it’s supposed to be serving.’
After the awards, held in London, Ms Mordaunt was greeted by a raft of online support.
Twitter user Simon Gardner said: ‘Best defence minister this country has ever had and a champion and ambassador to so many other causes. A very worthy winner in my opinion.’
Sue Pascoe added: ‘Congratulations and thank you for your speech and your fantastic time in post.’
Meanwhile Wes Knight said: ‘Congratulations to @PennyMordaunt – politician of the year 2019.
‘I do see a future prime minister in her. I wonder if there’s ever been a prime minister representing Portsmouth before? Best wishes to her and job well done.'
Other politicians shortlisted for the award were the Labour MP Angela Eagle, Liberal Democrats Kirsty Williams and Lord Paul Scriven, and John Blair – the first openly gay member of the Northern Irish Assembly.
Pink news is a UK-based online newspaper founded in 2005, marketed to the LGBTQ+ community worldwide.