As with previous equity sales, Carillion will reinvest the money in PPP projects and return one-third of the profit to shareholders as a dividend.
John McDonough, the chief executive of Carillion, said "As expected, there is a growing market for PPP equity and we intend to continue our phased programme of equity disposals."
Monday's announcement coincided with Laing's disclosure that it had signed a 50:50 joint-venture agreement with Commonwealth Bank of Australia.
The companies will co-invest in UK hospital and European roads projects. It will look at £300m of project equity investment over the next three-to-five years.
Laing chief executive Andy Friend said: "This co-investment partnership is an important building block in assembling a wider platform for growth at a time of significant market opportunity."
In a trading statement, Laing added that it expected to close six of the 15 contracts it had at preferred or sole bidder stage in the second half of the financial year.