The incumbent on the account was Walker Media, which resigned from the business last September.
The account is worth just under £1m, according to MPG Media Contacts, and the scope of the work covers offline and online channels in the UK.
Circle, which became the first private UK firm to run an NHS hospital last year when it won the tender to run Hinchingbrooke Hospital, plans to build a network of 30 hospitals across the UK in the coming years.
Paul Frampton, managing director, MPG Media Contacts, said: "We're proud to be working with Circle, which does an excellent job in the Healthcare sector.
"Our primary aim will be to deliver them an integrated media strategy that will bring them real value this year."