The sale of professional services firm Parsons Brinckerhoff to WSP Global comes five years after Balfour bought the business for £380 million.
Last month, Balfour's insistence that the disposal of Parsons went ahead helped to kill off Carillion's hopes of securing a £3 billion merger deal.
Balfour initially held talks with its rival but walked away due to Carillion's "wholly unexpected decision" to insist Parsons was included in the merger.
Up to £200 million of the proceeds from the sale will go to shareholders, with another £85 million helping to reduce Balfour's pension fund deficit.
Executive chairman Steve Marshall said the move delivered a "significant return" on the original investment and created value for its shareholders.
The group added it was now focused on restoring the fortunes of its UK construction arm, which has been at the heart of recent profits warnings.
Shares in Balfour opened 3% higher today.
Parsons employs 14,000 people worldwide and offers services including strategic consulting, planning and construction management.