Former minister Jo Swinson is running to replace Sir Vince Cable as leader of the Liberal Democrats.
Ms Swinson said she will lead a movement to tackle “nationalism and populism” after announcing her candidacy on BBC’s Question Time.
The party’s current deputy leader said she was the right person to lead the “liberal movement” following Sir Vince’s decision to stand down earlier this year.
The MP for East Dunbartonshire was first elected to Parliament aged 25 in 2005, becoming the first ever MP to be born in the 1980s.
Now 39, Ms Swinson also became the first MP to take her baby into a Commons debate when she took her second son Gabriel into a discussion on proxy voting in September 2018.
A former marketing manager, Ms Swinson rose to become a business minister and minister for women and equalities in the coalition government.
Ms Swinson lost her seat in the 2015 election to the SNP but won it back again in the 2017 election.
After former Lib Dem leader Tim Farron stood down Ms Swinson was named as one of the possible contenders but successfully ran for deputy leader instead. She is also the party’s shadow foreign secretary.
Ms Swinson married former Lib Dem MP Duncan Hames, who lost his seat at the 2015 General Election, in 2011.
She was made a CBE for political and public service and has has also written a book, Equal Power.