Metro, formed in 1993, has 140 staff and a turnover of £6.5m. Its clients include London Underground, Railtrack, train operating companies and rail suppliers.
The acquisition, for an undisclosed sum, has led to the creation of the Mouchel Metro division, which will be based in Metro's London office. The arm will have Metro founder Bill Bray as chief executive and former Railtrack director Brian Mellitt as chairman.
Stuart Black, Mouchel's business development director, said the division would offer a balance between long-term thinking for transport work and specific technical knowledge.
Black said: "The criticism of the rail industry has been that it is too fragmented. Anything that we can do even in a small way to bring a joined-up approach to manage the process could put the industry in better shape for the future."
Mouchel chief executive Jim Harding said: "We are setting out our stall. We want to be in the rail sector. We think we have something to contribute to Railtrack."
We are setting out our stall. We want to be in the rail sector. We think we have something to contribute to Railtrack
Jim Harding, chief executive, Mouchel
Harding added that the industry at present needed to concentrate on specific technical aspects of the rail systems rather than grand schemes.
"We need to look at delivering day-to-day bread-and-butter work to create a reliable system rather than just schemes such as the West Coast Mainline. A huge percentage of what delivers better quality service is about the day-to-day."
Harding said he had no immediate plans for floating Mouchel on the stock exchange. City sources reported last autumn that the firm was looking for a quick listing to raise resources for acquisitions.
Harding said: "No decisions have been taken about whether we float or not or when it may come about."