Giuliani Capital Advisors, which is chiefly an advisory body in bankruptcies and investment banking with revenues of $478 million in 2005, will be acquired by Macquarie for an undisclosed sum.
The acquisition, which is pending approval from regulatory bodies, will see Macquarie boost its presence in the US market from the 3,500 people it currently employs.
Commenting on the sale in a statement, Mr Giuliani said: "Joining the Macquarie team will allow the professionals of GCA to benefit from the vast resources of a leading global investment bank."
News of the deal comes in the week that Macquarie announced it had raised its predicted second-half earnings to $638 million from $494 million â a rise of 47 per cent.
Giuliani Capital's blue-chip clients have included stove manufacturer Aga and drug distributor Mckesson.
It is thought that Mr Giuliani is selling up so as to focus on his presidential ambitions.