The wind down of Weil, Gotshal & Manges marks the end of one of the legal market’s most influential M&A advisory platforms.

The collapse followed a wave of high-profile departures, including corporate chief Michael Aiello, one of the industry’s leading M&A rainmakers, who left with a team for Cravath, Swaine and Moore in September. His departure came amid a broader wave of exits and uncertainty over the firm’s future leadership. By late October, merger discussions with Willkie Farr & Gallagher had collapsed and Weil announced plans to wind down.

It brings an abrupt end to the 95-year-old law firm which advised on some of the world’s largest deals. Yet long before its final crisis, Weil’s share of M&A mandates had been steadily declining for much of the past decade, Mergermarket data shows.

Weil’s biggest M&A deals

Between 1 January 2016 to and the year-to-date (YTD) 2026 period covered by Mergermarket data, Weil advised on 2,804 deals, including both strategic M&A and private equity buyouts, with a combined value of USD 3.27tn.

Source: Mergermarket, data correct as at 03-Nov-26

The firm’s top deals in that period include advising NYSE-listed pharmaceutical company Allergan on its USD 86.6bn takeover by US biotech company AbbVie in 2019. More recently, the firm advised Microsoft on its USD 75.1bn takeover of Activision Blizzard which followed antitrust challenges in both the US and UK, in 2022.

The Weil team that advised Microsoft on the deal included Jenine Hulsmann, head of its European antitrust practice, who was profiled by Mergermarket‘s Trailblazing Women series this year.

The table highlights the scale and breadth of Weil’s M&A practice, with the firm advising some of the world’s largest companies across sectors including pharmaceuticals, technology, telecommunications and consumer goods, on both public and private M&A.

Weil’s historic role in M&A

Founded by three partners in New York in 1931, Weil grew to become one of the top corporate and litigation law firms in the world. After the Bankruptcy Reform Act of 1978 created the modern Chapter 11 framework in the US, Weil partner Harvey Miller built a practice group that came to dominate work for large distressed companies. His team’s work on landmark cases such as Lehman Brothers and Enron helped make Weil synonymous with large-scale restructurings, and showed large firms just how profitable that restructuring work can be.

Over subsequent decades, the firm expanded its corporate offering through building a transatlantic M&A powerhouse, advising Fortune 500 companies, blue-chip corporates and financial sponsors on headline takeovers, private equity buyouts and other transformational deals up until the time of its collapse.

The foundations date back to the late 1980s and 1990s where Weil started to build a reputation in the emerging private equity market. “When I was a junior, Weil had the best PE practice in the City,” reflected one leading partner at a rival firm.

By the 2000s, the firm had translated these sponsor relationships into a corporate machine, advising both strategics and sponsors on complex cross-border deals.

The 2007 hire of Aiello from Dewey Ballantine meant that the firm went on to build one of the strongest public company practices. Aiello advised on some of the most defining deals of the past 20 years, acting for clients like Sanofi, Procter & Gamble and The Home Depot.

Of the 10 biggest deals in Mergermarket‘s dataset (see table), he advised Reynolds American on its USD 64.1bn sale to British American Tobacco (BAT) in 2016, involving the 57.8% stake that BAT did not already own. He also acted for financial adviser Evercore in T-Mobile’s USD 68bn merger with Sprint.

Alongside its public company work, Weil maintained one of the legal market’s most prominent sponsor-side M&A practices. The firm is known for having key PE relationships with some of the world’s largest sponsors including Advent and Bain Capital.

One of the leading figures in that practice was Christopher Machera, who co-headed Weil’s US private equity practice and advised sponsors including Blackstone, CVC and TPG. He also left Weil weeks before Aiello, for Paul, Weiss, Rifkind, Wharton & Garrison.

By October 2026, the loss of leaders and partners from both sides of its corporate practice in the US, as well as a string of departures in London, including M&A leader David Avery-Gee to Sullivan & Cromwell, meant Weil was showing visible signs of strain.

Weil’s role in strategic deals

Weil’s market share advising on strategic deals – advising either an acquiror or target – where no sponsor is involved, gradually declined over the past decade according to Mergermarket data.

The firm’s market share was considerably higher in 2016 and 2019 than in the years that followed. Its weakest performances came in 2023, 2024 and 2025, which recorded the lowest figures of the period.

2026 year to date (YTD) was showing some improvement, with Weil accounting for 4.6% of the market. This is its strongest performance since 2022, although it remains well below the levels achieved earlier in the decade.

One former Weil partner said the firm had increasingly focused on winning larger transactions, rather than competing with firms such as Kirkland & Ellis on deal volume.

Weil’s role in PE buyouts

Weil was also losing ground advising on private equity buyouts. 2024 points to its lowest figure, where market share was at 3.5%.

The double-digit figures that Weil enjoyed prior to 2023 had declined, although 2025 was the highest figure at 9.23% since then.

Among its prominent sponsor side transactions include Refinitiv, where Weil advised Blackstone on the USD 17.5bn carve out from Thomson Reuters, alongside CPPIB and GIC, in 2018.

How Weil compared with its rivals

For much of the past decade, Weil held a place among the top 20 for law firms globally. In 2016, it ranked sixth, putting it close to the very top of the market.

Source: Mergermarket, data correct as at 03-Nov-26. YTD through 03 Nov for each year shown.

But from 2022, the firm began to slip down the rankings. That contrasted with rivals such as Kirkland & Ellis, Latham & Watkins, Sullivan & Cromwell and Skadden, which remained difficult to dislodge from top positions.

Firms like this had continued to build out their M&A practices, hiring key partners and expanding their teams to compete for more mandates. Weil, by contrast, appeared less willing to grow “because the star partners wanted to keep it tight,” said one former Weil partner.

The question is now where the work will go. Cravath, Paul Weiss, Sullivan & Cromwell, Simpson Thacher and Gibson Dunn are among the firms that have already begun hiring Weil lawyers.

Hiring former Weil partners and teams gives them a head start in pursuing the firm’s former clients and mandates. But clients will decide which law firms are best placed to handle their transactions, and other established M&A firms will be competing for the same mandates.

Weil’s collapse leaves a significant gap in the M&A market, and its rivals are wasting no time looking to fill it.