Almost 16.36 million shares were sold at 775 pence each in a placing run by Credit Suisse and JP Morgan Cazenove.
The sale – on behalf of the Wood Family Trust, the Sir Ian Clark Wood's 1997 Discretionary Trust and members of the Wood family – was equivalent to 4.4% of issued share capital of the oil services giant.
Confirmation of the sale sent Wood Group's share price down 35p, or 4.29%, to 780p marking it as the biggest faller in the FTSE.
Around £130m was knocked off the market capitalisation, leaving its worth at £2.9 billion.
The recently retired Sir Ian Wood holds more than nine million ordinary shares, equivalent to 2.4% of Wood Group's share capital, and is understood to have no current intention to sell or transfer them.
The 70-year-old retired from the board on October 31 after spending 45 years as either chief executive or chairman.
In June last year trusts established for the benefit of members of the Wood family and for charitable causes offloaded 58 million shares in Wood Group, 10.6% of the total shares at the time, for £365m.
Also yesterday, Wood Group, now headed by chairman Allister Langlands and chief executive Bob Keiller, was appointed to design a 230km pipeline to export gas from the Chevron-operated Rosebank development West of Shetland. The gas pipeline will be connected to the Shetland Islands Regional Gas Export line and then to the St Fergus terminal.