Borwick replaces Richard Barnes who lost his Assembly seat at last week’s election.
By law the Deputy Mayor must be a member of the London Assembly and only it and the Deputy Mayor for Policing are legally recognised positions.
All other ‘deputy mayors’ hold honourific titles only designed to signal the Mayor’s interest in a given policy area.
Borwick was re-elected to the Assembly last week to one of the 11 London list ‘top-up’ seats which are allocated to ensure overall representation on the Assembly reflects the parties shares of the vote.
Placed third on the list of Conservative list candidates, Borwick previously suggested she did not expect to be re-elected. However the loss of two constituency seats meant the Conservatives kept all three of the top-up seats won in 2008.
In 2000 Borwick was running-mate to Conservative Mayoral candidate Steve Norris.
Announcing the appointment Mr Johnson said: “’Victoria Borwick’s track record on the London Assembly makes her the perfect candidate to be my Statutory Deputy Mayor and I know she will do an outstanding job in that role.”
Borwick said: “It is an honour to be appointed statutory Deputy Mayor and I am delighted to have been given the opportunity to make the capital a better place to live and work for all Londoners and to help make a real difference to the greatest city in the world.”
The Mayor has also confirmed a number of other appointments for his second-term team including AM James Cleverly who will Chair the London Regional Resilience Forum and has been proposed as Chair of London Fire and Emergency Planning Authority (LfEPA).
Johnson said Cleverly would “demonstrate great ability” in the roles.
Other appointments include Isabel Dedring as Deputy Chair of Transport for London and Deputy Mayor for Transport and Daniel Moylan as Chair of the new London Legacy Development Corporation.
The Mayor also confirmed that Daniel Ritterband will continue in his role as Director of Marketing and 2012 Communications, overseeing all London Games-related communication.