Sources close to both firms denied that the deal would lead to large-scale staff cuts or the closure of Babtie's Glasgow headquarters. One source said: "It's about growing the two businesses, not slashing them."
Jacobs, which has 35,000 employees worldwide and a turnover of £2.7bn, said the deal was part of plans to become a global leader in the infrastructure market.
Chief executive officer Noel Watson said: "I would expect to see the Babtie team being a key part of out leadership globally in building this business."
Babtie posted a pre-tax profit of £7.8m for the year to 31 December 2003 on turnover of £179m. In April Babtie said it wanted to double turnover in five years.
The firm has offices in Ireland, the Czech Republic, India, Singapore and Hong Kong.