His appointment is effective 2 September, with Brooks (formerly Wade) editing her final edition of newspaper on 1 September.
Mohan has worked on the newspaper for 13 years and was most recently appointed to the position of deputy editor in 2007.
Prior to this, he spent three years as associate editor of features, and previously, two years as assistant editor. He started his career at The Sun on its showbiz column, Bizarre.
He joined paper from sister publication News of the World where he was a reporter.
Brooks will take responsibility for the day-to-day operations of News International and its titles The Sun, News of the World, The Times and The Sunday Times.
She will continue to report to chairman and chief executive of parent company News Corp Europe and Asia, James Murdoch. He now also takes the title of executive chairman of News International.
The Sun has recently restored its average net circulation above 3 million after a few dips this year thanks to price cutting and promotions. The title is currently 20 pence in the Carlton region.
Meanwhile, the publisher this month announced plans to close thelondonpaper, its free evening newspaper, after it recorded a pre-tax loss of £12.9m in the year to 29 June 2008.