Dr Bull, a former practising doctor and deputy chair of the party, initially joined Nigel Farage's team as an MEP for the Brexit Party in 2019.
His appointment aims to bring internal stability to Reform UK and attract potential donors, addressing issues that arose during Mr Yusuf's chairmanship.
Before entering politics, Mr Bull had a career as a TV presenter, including roles on shows like Most Haunted Live!, Newsround, and Call the Doctor.
Bull's political involvement includes an unsuccessful run as a Conservative Party candidate in 2010, followed by joining the Brexit Party in 2019 and later becoming an MEP; he currently presents on TalkTV.