Carlaw served as acting Leader of the Scottish Conservative Party from September 2018 to May 2019 during Ruth Davidson's maternity leave and from August 2019 to February 2020 following Davidson's resignation as leader. He was elected Scottish Conservative leader in the February 2020 leadership election, winning more than three-quarters of votes from party members. He resigned the leadership in July 2020, stating he was not the person best placed to lead the party into the 2021 Scottish Parliament election.