Aon is to move its London operation to the The Leadenhall Building, dubbed the 'Cheesegrater tower'.
The broker is taking up ten floors of the building, which will be known as The Aon Centre, from early 2015.
Aon agreed non-binding heads of terms with developers The British Land Company and Oxford Properties for a 191,000 sq ft pre-let of the 610,000 sq ft building.
Aon chief executive Rob Brown said: “We are delighted to have chosen The Leadenhall Building as our new London headquarters.
"The Aon Centre at The Leadenhall Building is an impressive location and the offices will reflect our position as the leading global professional services firm focused on risk and human capital management."
He added: "Such a significant investment confirms Aon Corp’s commitment to the UK, and indeed London, as a strategically important and integral part of Aon’s future. We look forwardto working with British Land and Oxford Properties.”
As well as the lower 10 floors of the offices (levels 4-13), Aon also has options to take up to a further 85,000 sq ft of space on levels 14-18.
The 736 ft (224m), 47 storey Leadenhall Building's completion is scheduled for mid 2014. It is currently under construction in the City of London opposite the Lloyd's building.
Chris Grigg, chief executive of British Land said: “We are delighted that Aon has chosen The Leadenhall Building as the headquarters for its UK operations."