Mr Johnson announced that councillor Mary O'Connor will work alongside him in the fight against health inequalities in the capital.
Ms O'Connor was previously a senior nurse at Ealing Hospital and has been a councillor at the London Borough of Hillingdon since 2002.
Johnson has cited health improvements as one of his main priorities. He said: ‘Reducing health inequalities is one of the biggest challenges facing London.'
Ms O'Connor said: ‘Everyone in our city should have the same opportunities to lead healthy, active and productive lives. We have exciting opportunities for action.’