KBR received a contract in March from the US Army Corps of Engineers to fight oil well fires in Iraq, repair the oil infrastructure and provide other support services for the US military.
Halliburton said the vehicle hit an anti-tank mine while on a routine run carrying post from Baghdad to northern Iraq.
The victim was part of a team that supported a US army project called Material Logcap III. Under the contract KBR provides a range of services to the army from building base camps to delivering the soldiers' post.
More than 50 American soldiers have been killed by hostile fire since President Bush declared the war to be over in May.
Consulting engineer Halcrow is leading the British push to win reconstruction contracts in Iraq. Last month, the company established an office in Basra after it was awarded a contract to look into water supplies by the Department of International Development.
A Halcrow spokesperson said the company did not intend to withdraw any employees from Iraq.
The spokesperson said: "The personal security of our staff in Iraq is of paramount importance to Halcrow. All of our people in Baghdad and Basra have undergone extensive hostile environment training."