Sir Simon Milton described the offer to be Mr Johnson's deputy as "irresistible"
The Mayor of London Boris Johnson has nominated the leader of the Local Government Association (LGA) as his new deputy mayor.
Sir Simon Milton, who is stepping down as LGA chairman and as a Westminster councillor, is to be responsible for planning and policy.
His appointment follows the departure of deputy mayor Ray Lewis amid claims of financial irregularities.
The appointment is subject to approval from the London Assembly.
Sir Simon said the offer was "irresistible".
"I believe that I can make a significant contribution to making Londoners' lives better and making Boris Johnson's Mayoralty a success," he said.
The LGA will elect another chairman who is expected to take up the post in September.
Mr Johnson initially defended Mr Lewis amid multiple claims relating to his time as a vicar and as founder of an academy for young people.
However, he was forced to step down after it emerged the mayor had been told wrongly that Mr Lewis was a serving justice of the peace.
Mr Lewis denies all allegations and has never been charged with a criminal offence.
An independent inquiry was launched in City Hall into the claims, but was scrapped after Mr Lewis resigned earlier month.