Haymills was expected to enter administration briefly on Wednesday morning before signing the deal to with Vinci.
Staff on weekly wages were expected to be paid their arrears over the next few days, with those on monthly salaries soon after. The majority of the 700 or so jobs at the firm looked likely to be saved, although some redundancies appeared inevitable.
Sub-contractor payment was due to be approached on a case-by-case basis, with the firm battling to keep as many contracts as it could.
A source at Haymills said the mood among employees was mixed.
“We had a staff meeting on Tuesday morning and were talking about the next steps. Most of the staff were aware of what was going to happen,” said the source.
“There is a mixed bag of emotions. It is part relief, but this is going to be an incredible change for a lot of people.”
Vinci was created in 1899 by French engineers Alexandre Giros and Louis Loucheur, and has become one of the largest construction firms in the world. It has a worldwide turnover of €33.5 billion (£28.7bn), and employs 164,000 people.
Its UK operations now put it into the top 10 contractors this side of the Channel. The acquisition of Haymills would put it on the verge of a top five spot.
Vinci has acquired a number of regional UK contractors over the past few years. In January 2008, it bought Cardiff-based contractor Stradform, and a few weeks later it acquired Newcastle-based Gordon Durham.
Last September, Vinci acquired housebuilder Taylor Wimpey’s contracting arm Taylor Woodrow for £74 million.
Haymills – which had a turnover of £181.2m for the year ended 31 March 2008 – had been the subject of intense speculation since putting its Gibraltar arm into voluntary liquidation last week.
It was forced to delay payment of staff wages and money owed to sub-contractors after RBS removed its overdraft facility.
An administrator-elect was given four offers to choose from on Friday. Vinci – said to have been Haymill’s favoured buyer as it would save the most work and jobs – was said to be tying up paperwork on Tuesday evening.
The company largely blamed RBS for its problems.
“As far as we are concerned, RBS reneged on a deal with us. An honest, hardworking company is in the situation it finds itself in because a bank owned by the people has reneged on an agreement.”
The bank has declined to comment.