A native of Biggar, Regan moved to Devon, England, and studied international relations at Keele University in Staffordshire.

She first got involved in politics when she became head of campaigns and advocacy at the Common Weal, a left-wing pro-Scottish independence think tank.

In the aftermath of the referendum defeat, she joined the SNP and was later selected as a candidate for the Edinburgh Eastern constituency in the 2016 Scottish Parliament election.

After a successful campaign, she sat as a backbencher, before being appointed to the Scottish Government in First Minister Nicola Sturgeon's 2018 cabinet reshuffle.

[5] Regan attended primary school in Scotland, before moving with her family to North Devon in England aged ten.

[6][7] When she was fifteen years old, Regan changed her birth forename in a deed poll to Ashten, to avoid confusion with another girl in her school who shared the same name.

Her then husband, who was born in England, assumed Regan would vote 'No'; however, after she conducted research she had found herself to be more leaning towards the 'Yes' movement.

In August 2015, she was selected as the SNP candidate for the Edinburgh Eastern constituency in the upcoming 2016 Scottish Parliament elections after the incumbent MSP Kenny MacAskill, had announced in June that he would not stand for re-election.

In June 2016, Regan was appointed as Parliamentary Liaison Officer to the Cabinet Secretary for Culture, Tourism and External Affairs.

[22] Later that month, an exchange between Regan and fellow SNP MSPs Gillian Martin and Ruth Maguire was leaked.

[23][24] In June 2019, it was reported that some of her ex-employees received pay-offs worth thousands of pounds and some signed non-disclosure agreements.

[28] On 27 October 2022 Regan resigned, citing concerns over the Scottish Government's support for the Gender Recognition Reform Bill.

With Regan's support, Yousaf could force the motion to a tie, which would by convention, be then defeated by the Presiding Officer's vote in favour of the status quo.

[38] She sent a list of demands to Yousaf in exchange for her support; these included progress on independence, and protecting the rights of women and girls.

[46] Regan personally supports the establishment of a Scottish republic, while the official SNP position during her membership was to retain the British monarch as head of state in an independent Scotland.

[48] Regan said she wanted to slow down plans to achieve net zero carbon emissions by phasing out extraction of oil and natural gas from the North Sea.