Skanska has been confirmed as contractor for a new-build prison at Belmarsh West in London.
The firm is the construction partner of Serco, which has signed a contract with the Ministry of Justice to run Belmarsh West, under a design, construct, manage and finance arrangement.
The contract has a value to Serco of approximately £415m, and will run for 26.5 years.
The prison, which will be built to Category B standards by Skanska, will accommodate 900 adult male prisoners.
Construction work will begin immediately, with completion expected in the first half of 2012.
Skanska has worked with Serco since 1994 on prison projects.
This is the first prison contract to be awarded in the UK to an alliance of the private and voluntary sectors. Turning Point and Catch22 will work with Serco to prepare inmates for release.
Serco had previously announced its selection, in June 2009, as the preferred bidder to provide and operate two new prisons at Belmarsh West, and at Maghull, Liverpool.
It said it expects the contract to provide and operate the prison at Maghull will be signed later this year.