Mountfield revealed neither the client nor the precise location, saying only that it was a £4.5m contract to supply and install raised access flooring at a newly constructed office development in the City of London.
Work is scheduled to start in January 2015 and to continue through to the end of the first quarter of 2016.
Connaught managing director Andy Collins said: "This contract appointment, coming shortly after the successful completion of the substantial data centre fit out in Scandinavia, represents another important step in the development of Connaught. Not only is it the largest contract that has been awarded to Connaught, but winning it against strong competition has underlined our position as a market leader in this increasingly important sector of the flooring market. That position has been achieved through the quality of our offering to clients and our reputation for consistently delivering demanding and complex contracts on time and within budget constraints."
Connaught was acquired by Mountfield in 2008.