The two-year contract has been awarded by Lukoil of Russia, and is for the provision of general maintenance services for the West Qurna-2 oilfield in southern Iraq.
Glasgow-based Weir described West Qurna-2 as one of the largest undeveloped oilfields in the world.
Weir said that, under the agreement, its engineers would deliver mechanical, electrical, maintenance and pipeline services for the related production facilities, including the Mishrif Central Processing Plant.
The company highlighted the fact that it had invested more than $8m (£4.8m) in establishing its service centre in the Iraqi port city of Basra, where it has been operating since 2010.
Weir declared that this was the first in-country location to offer fully comprehensive maintenance services for all kinds of rotating equipment, valves and wellheads in Iraq.
A spokesman for Weir said about 120 people would be employed on the contract. Around half would be Iraqi nationals, he added, and the rest would be from many different countries, with Scots among those who would work on the project.
Mishrif will produce 150,000 barrels of oil per day initially, Weir noted. Output is expected to rise to 400,000 barrels of oil per day by the end of 2014.
Weir added that the processing facility was expected to be operational in the first half of this year, at which time it would commence work under the terms of the contract.
Keith Cochrane, chief executive of Weir, said: "This substantial contract demonstrates the importance of Weir's long experience of working in Iraq, and our reputation for delivering high-quality engineering services in support of the country's developing oilfield infrastructure."
He added: "It also reflects our global capability, a key strength of our group which allows us to capture opportunities in high-growth markets and be a partner of choice to our worldwide customers."
The West Qurna-2 oilfield was discovered in 1973 and explored, through the collection of two-dimensional seismic survey data and exploratory drilling, in the 1970s and 1980s by Soviet exploration and service companies.
Weir said the West Qurna-2 area was about 300 square kilometres.
West Qurna-2 is being operated by a consortium comprising Lukoil, which has a 75% stake, and the Iraqi state South Oil Company, with 25%.
Weir's annual revenues exceeded £2.5 billion in 2012, of which more than half came from the provision of services and after-market support.
Emerging markets contributed more than 40% of Weir's orders in 2012.
The engineering group's oil and gas division employs more than 3000 people and racked up revenues in excess of £800m in 2012.
Weir, founded in 1871, highlighted the fact that its oil and gas division had been providing equipment and services to the Middle East since the early 1900s.
Shares in Weir yesterday dipped by 50p or 2.3% to £20.90, in spite of news of the contract win, as the UK stock market tumbled.