O’Donnell will join Hotwire’s six-person global leadership team and reports into global CEO Barbara Bates.
She will lead a team of 80 staff in London and takes over from interim MD Adele Breen, who has been in post for six months following Matt Cross’ move to a newly created role of head of B2B, EMEA.
Breen will now take up the post of head of UK client services and reports into O’Donnell.
"To appoint a new MD, the calibre of Tara, at a time when our UK business is coming off another record year of double-digit growth, sets an exciting tone for our London business," Bates said.
"Her success leading Text 100's UK business through a period of growth, her consumer and entertainment background and her previous client-side work gives our clients and our team access to incredibly diverse expertise."
O’Donnell added: "I’ve been looking for the next stage of my career since leaving Archetype and through all the conversations with Barbara and her senior team, I’ve been struck both by the calibre of the people but also the strong culture that runs through the firm. I’m thrilled to be joining a talented London team, Hotwire’s largest global office."