The takeover is yet to be approved by the German competition authority, but it would follow Van Oord's acquisition of fellow Dutch offshore wind contractor Ballast Nedam Offshore from its parent company, in 2014.
Bilfinger announced its intention to sell the offshore unit in February 2015, following an "unsatisfactory" financial year. The firm said the unit fell outside of its "risk profile".
"Both investments are part of our strategy to bolster our position on the northwestern European market for offshore wind projects. Acquiring Bilfinger's offshore wind activities will enable us to focus more on the German market," said CEO Pieter van Oord.
Van Oord also said it was upgrading its Aeolus installation vessel with a larger capacity crane in order to accommodate larger foundations and heavier turbines, a continuing trend in offshore wind.
The firm recently completed the installation of foundations at Dong Energy's Burbo Bank Extension project in the UK. It also has a vessel at the 600MW Gemini project off the Netherlands.
Bilfinger has previously won contracts at Wpd's Nordergrunde project and Vattenfall's Sandbank site.