Irish investor Michael Whelan has appointed CB Richard Ellis to sell Victoria House on Southampton Row.
The Bloomsbury property is likely to be sold between £170m and £180m at a yield between 6.5%-7%.
Whelan bought the property from German property company Garbe for £160m in 2004 as Irish investors poured in the UK market during the boom.
At the time it was thought Michael Whelan was buying Victoria House as an investment for his children through a wholly owned company called Lunar Sea Properties. Whelan is a well-known figure in Ireland, mainly through his development company Maplewood Developments, a big housebuilder in the Irish Republic.
Victoria House totals 215,300 sq ft of offices, plus 77,000 sq ft of retail and leisure.