Global giant Norton Rose Fulbright and Manhattan-based Chadbourne & Parke have finalised their merger, ending Chadbourne's 115-year run as an independent firm.

The combined firm, which will shed the Chadbourne name and operate internationally as Norton Rose Fulbright, has about 4,000 lawyers in 58 offices and 32 countries, generating up to $2bn in annual revenues.

The combined firm has more than 1,000 lawyers in the US, the firms said when they announced their merger plans in February. With about 300 lawyers in New York alone, post-merger Norton Rose Fulbright will rank among Manhattan's 25 largest law offices, and it will also have more than 130 lawyers in Washington DC.

Despite client conflict issues, the firms have managed to close the deal on the last day of the second quarter of 2017 – within the original timeline announced for the deal.

The combination creates a firm with particular strengths in the energy, project finance and infrastructure sectors and disputes.

"Bringing together Norton Rose Fulbright and Chadbourne will enable Norton Rose Fulbright to provide even greater breadth and depth of services to our clients," said Peter Martyr, Norton Rose Fulbright's global chief executive, in a statement. "We now offer enhanced capabilities in New York and Washington DC, while our global platform expands to Mexico City, São Paulo and Istanbul."

Andrew Giaccia, the combined firm's US management committee vice-chair and Chadbourne's former leader, said in a statement: "Our lawyers' shared commitment to client service – along with our strong compatibilities in the areas of energy and infrastructure, banking, corporate and finance, project finance, bankruptcy and restructuring, litigation and regulatory law – makes this a powerful combination."

The merger hasn't been welcomed by all. In the more than four months since the merger discussions were confirmed, nearly 50 lawyers have left Chadbourne, including 18 partners and a team that went to Covington & Burling. About 273 lawyers have exited Norton Rose firmwide, according to figures from Legal Week's US intelligence arm, which tracks lawyer moves. Normal attrition likely accounts for a portion of the departures at both firms.

The firms' complimentary practices in energy, project finance and infrastructure could be a boon as the legal industry struggles with flat demand. Both firms' gross revenues have fallen in each of the past three years, according to American Lawyer financial reporting.

Chadbourne's revenue dropped by 6.6% to $232.5m last year. Amid a string of lateral exits and a (still ongoing) high profile discrimination suit against the firm, lawyer headcount dropped by 9.4% to 288 in 2016, while profits per partner grew 2.6% to $1.165m.

Norton Rose Fulbright posted global revenue of $1.685bn in 2016, down about 3% from the prior year.

A fading New York firm

Chadbourne becomes the latest storied New York firm to lose its name in a merger with a larger competitor, echoing the combination between Rogers & Wells and Clifford Chance.

In 1997, Chadbourne peaked at 41 on the Am Law 100 rankings of the highest grossing firms in the US. Back then it was best known for its representation of British American Tobacco in product liability litigation.

The firm, founded in 1902 in New York City by premier dealmaker Thomas Chadbourne, represented the Wright Brothers, James Joyce, Winston Churchill and Howard Hughes.

In one its best-known cases, Chadbourne represented Brown & Williamson in its standoff with whistleblower Jeffrey Wigand, a fight made famous in the 1999 film The Insider. It advised on the merger between the American Football League and National Football League in the 1960s, and represented John Edwards in his campaign finance trial in 2012.

By 2006, when the heyday of tobacco litigation was passing, Chadbourne had slipped to near the bottom of The Am Law 100. But as The American Lawyer reported then, the firm's glacial speed in reacting to its declining status in the marketplace was another factor in its diminishing size. In 2013, Chadbourne & Parke fell out of The Am Law 100 .

In linking up with Norton Rose, Chadbourne attorneys will now have a platform within the top 20 of the Global 100 firms.

Norton Rose, the product of a 2013 mega-merger between Houston-based Fulbright & Jaworski and London-based Norton Rose, has expansion plans beyond Chadbourne. Since the February merger announcement with Chadbourne, the Swiss verein announced plans to unite with Australia's Henry Davis York.

In New York, Chadbourne and Norton Rose share the same office building at 1301 Sixth Avenue, where Chadbourne signed a 20-year lease in 2012.

However, a number of Chadbourne lawyers have opted against the merger, with Covington & Burling announcing the hire this month of a team of 15 Chadbourne lawyers, including two London international partners, after recruiting a four-partner project finance team from the firm earlier this year.

Earlier this month, Legal Week reported the merger was facing delays due to client conflicts.

Norton Rose chief executive Peter Martyr said at the time: "The combination process included an in-depth review of potential conflicts. We have identified very few material conflicts and are working to resolve these.

It is understood that project finance was among the groups affected by client conflicts.

Norton Rose has been through a succession of major mergers. It merged with Australian firm Deacons in 2010, then in 2011 with Canadian firm Ogilvy Renault and leading South African firm Deneys Reitz. These were followed by a second Canadian merger with Calgary's Macleod Dixon in 2012, while legacy Norton Rose's union with US firm Fulbright & Jaworski went live in summer 2013. The firm also inked a deal with Vancouver-based firm Bull Housser & Tupper in September 2016.