The presenter has linked up with the City and sport consultancy after bringing an end to his 13-year broadcasting career.
Before joining the BBC in 1997, Alexander was sports editor of three national newspapers, the Mail on Sunday, The Sun and the London Evening Standard.
‘Brian is one of the best connected and most respected sports journalists in the business,’ said David Bick, chairman of Square 1. ‘He will bring his contacts, knowledge and experience to us and work on a range of projects, both in sport and in finance.’
During his career at the BBC, Alexander launched and presented the Sunday morning show Sportsweek, followed by stints hosting Late Night Live and Weekend Breakfast.
For the past four years he has been presenting and creating a series of Sport Specials, including agenda-leading investigations and interviews with some of the biggest names in world sport.
His last two were exclusive one-on-ones with FIFA president Sepp Blatter and former Liverpool manager Rafa Benitez.
In recent years, Alexander has established himself as a media trainer, with clients including LOCOG, organisers of London 2012, other sports organisations and a number of banks and City institutions.