Shoosmiths - which advised Vivergo Fuels on the UK's largest biorefinery - was among guests invited to attend the official opening of the £350m plant.
The national law firm provided real estate, development, planning, construction, environmental, tax, employment, commercial agreement and litigation advice regarding the biorefinery, near Hull.
Partners Graham Bennett - who led the legal team - and Simon Wain - who led the construction team - were among 60 guests at Monday's opening at Saltend Chemicals Park, performed by Vince Cable MP, Secretary of State for Business, Innovation and Skills.
The biorefinery, which began production in late 2012, will turn 1.1m tonnes of UK feed-grade wheat into bioethanol every year, while co-products are converted into 500,000 tonnes of animal feed, thus largely eliminating all waste.
The bioethanol will be blended with petrol to meet Government targets under the Renewable Transport Fuel Obligation. In addition to the UK the business will also supply the greater European market.
Bennett, who specialises in large-scale real estate development, acquisition, leasing, financing and disposal work, has wide-ranging experience of riparian and coastal projects, including Chatham Docks, the Rochester Riverside regeneration, and the Gateway to Portsmouth project. Saltend Chemicals Park is on the bank of the River Humber.
Construction lawyer Wain advised on construction contracts, including drafting and negotiation of a bespoke engineering, procurement, and construction management contract.
Partners and commercial specialist Andrew Pickin also advised on a suite of commercial agreements necessary to underpin the start-up and operation of the plant.
Bennett said: "This is another fine example of Shoosmiths coordinating expertise from a range of disciplines on a complex, large-scale, economically important project.
"Bringing it to fruition has involved resolving numerous challenges, and we've much enjoyed working with the very supportive management team throughout the whole process."
Once fully operational, Vivergo Fuels will be among Europe's largest bioethanol producers, and will be the UK's biggest single-source supplier of animal feed.