The deal was finalised at a court hearing yesterday at 547.5 pence per share - four per cent less than the 570 pence Carillion offered a month before, which was rejected as too low.
The Office of Fair Trading approved the deal last Friday as it decided not to refer the proposed acquisition to the Competition Commission.
Carillion chief executive John McDonough said: “The acquisition of Alfred McAlpine is a major milestone in Carillion's development.
“The combined Group will be one of the UK's foremost support services businesses, with significantly enhanced capabilities to provide integrated solutions for services, buildings and infrastructure, from private finance to life-time asset management.
“With an order book in the region of £20 billion and well established positions in a wide range of growth markets, Carillion is well placed to continue its strong momentum in 2008 and over the medium term.'
Alfred McAlpine shares and listing on the London Stock Exchange was cancelled from 8am this morning.