Contested mergers and acquisitions have evolved from a peripheral concern for corporate legal teams into a central, durable feature of the American public-company landscape. A comprehensive new report released by Diligent Market Intelligence, produced in collaboration with the law firm Seward & Kissel, reveals that shareholder activism targeting M&A transactions has reached a critical inflection point. By analyzing nearly 300 activist demands opposing the sale of U.S.-listed companies since 2015, the report highlights a significant shift in investor behavior and board-level vulnerability. Drawing upon Diligent’s extensive datasets regarding activism, voting, and governance, the findings indicate that activist success rates in blocking or altering deals reached their highest level in 2025 since the previous peak in 2018.
The phenomenon of "deals in dispute" encompasses a variety of activist strategies, ranging from "bumpitrage"—the practice of buying shares after a deal announcement to agitate for a higher price—to outright opposition aimed at keeping a company independent or seeking an alternative suitor. As the M&A environment faces headwinds from regulatory scrutiny and fluctuating interest rates, the Diligent report underscores that boards of directors must now treat activist intervention as an expected, rather than exceptional, component of the deal-making process.
The Evolution of M&A Activism: A Decade of Conflict
To understand the current surge in contested deals, it is necessary to examine the trajectory of shareholder activism over the past decade. Historically, activist investors focused primarily on balance sheet optimization, such as demanding stock buybacks or dividend increases, and board representation. However, as traditional avenues for value creation became more crowded, activists increasingly turned their attention to the "event-driven" space of M&A.
Between 2015 and 2018, the market saw a steady rise in activists challenging deal terms, often arguing that boards were "leaving money on the table" or failing to conduct a sufficiently robust "go-shop" period. This era was characterized by high-profile battles involving major hedge funds that utilized sophisticated media campaigns to turn institutional investors against proposed mergers. Following a brief cooling period during the height of the COVID-19 pandemic—during which many companies focused on survival rather than expansion—activism returned with renewed vigor as the economy reopened and valuation gaps widened.
The year 2025 stands out in the report’s data as a landmark year for activist efficacy. The success rate for activists opposing or seeking to modify announced deals has hit its highest point in seven years. This resurgence is attributed to several factors, including the increased sophistication of retail investors, the more aggressive stance of proxy advisory firms, and a broader market sentiment that has become more skeptical of "empire-building" acquisitions that do not offer immediate, quantifiable synergies.
Chronology of Key Market Shifts (2015–2025)
The timeline of M&A activism reflects broader macroeconomic trends and shifts in corporate governance.
- 2015–2017: The Rise of Bumpitrage. Activists began specializing in identifying "low-ball" offers. By acquiring significant stakes post-announcement, they could leverage their voting power to demand price increases.
- 2018: The First Peak. A record number of deals were abandoned or restructured due to shareholder pressure, setting a benchmark for activist influence that would hold for several years.
- 2019–2021: Tactical Diversification. Activists began focusing on "broken" deals and ESG (Environmental, Social, and Governance) considerations, using sustainability metrics as a lever to oppose acquisitions in carbon-intensive industries.
- 2022–2023: The Valuation Gap. As interest rates rose, the gap between what sellers expected and what buyers were willing to pay widened. Activists exploited this volatility, claiming that boards were selling at the "bottom of the market."
- 2024–2025: The New High. The implementation of Universal Proxy Cards (UPC) and a more litigious environment provided activists with new tools to challenge boards, culminating in the highest success rates for contested deals since 2018.
Supporting Data: Analyzing the 300 Demands
The Diligent and Seward & Kissel report is based on a granular analysis of 298 specific activist demands involving U.S. companies. The data reveals several startling trends regarding the nature of these disputes.
Firstly, the sector-specific data suggests that technology and healthcare companies are the most frequent targets of M&A activism. These industries often feature complex valuations based on future growth rather than current cash flow, providing ample room for activists to argue that a proposed sale price undervalues the company’s long-term potential. In 2025 alone, technology companies accounted for approximately 35% of all contested M&A demands.
Secondly, the "success" of these demands is no longer defined solely by stopping a deal. The report categorizes success into three tiers:
- Price Improvements: The activist successfully forces the buyer to increase the offer price (the most common outcome).
- Deal Termination: The proposed merger is abandoned entirely, often followed by a change in management or a refreshed independent strategy.
- Governance Concessions: The deal proceeds, but the activist secures board seats or changes to the post-merger governance structure.
The data indicates that in 2025, nearly 48% of activist demands resulted in at least one of these favorable outcomes for the challenger, a significant increase from the 30-35% range observed in the early 2020s.
Official Responses and Strategic Implications
Legal experts and market participants have noted that the findings in the Diligent report should serve as a "wake-up call" for corporate boards. Seward & Kissel, a firm with deep expertise in investment management and corporate law, suggests that the increased success of activists is partly due to better preparation and more compelling narratives.
"Activists are no longer just looking at the numbers; they are telling a story about missed opportunities and failed oversight," noted a legal analyst familiar with the report’s findings. "When an activist can demonstrate that a board did not explore all strategic alternatives, or that the ‘special committee’ formed to evaluate the deal was not truly independent, they win the hearts and minds of the larger institutional shareholders like BlackRock and Vanguard."
Institutional investors, who hold the majority of shares in most U.S.-listed companies, have also adjusted their stance. While they once reflexively supported management in merger votes, many now utilize the data provided by firms like Diligent to conduct their own independent valuations. This shift has made it much harder for boards to "push through" a deal that lacks a clear, premium valuation.
In response to this environment, many corporate boards have begun adopting "activism-ready" protocols. These include performing "vulnerability assessments" before a deal is even announced and maintaining a "shelf" poison pill that can be quickly deployed to prevent an activist from building a blocking stake.
Broader Impact and the Future of Corporate Governance
The implications of the "Deals in Dispute" report extend beyond the immediate financial outcomes of individual mergers. The trend of heightened M&A activism is reshaping the fundamental relationship between boards and shareholders.
One of the most significant impacts is the "chilling effect" on certain types of transactions. Private equity firms and corporate acquirers are becoming more cautious, knowing that any deal they propose will be subjected to intense public scrutiny and potential litigation. This has led to longer negotiation periods and more robust "fairness opinions" from investment banks.
Furthermore, the rise of M&A activism is driving a change in board composition. To defend against activist claims of insularity, boards are increasingly seeking directors with specific M&A and industry expertise who can stand up to the rigorous questioning of hedge fund managers. The "Universal Proxy Card" rules, which allow shareholders to mix and match candidates from both management and activist slates, have only accelerated this trend.
Looking ahead to the remainder of 2026 and beyond, the report predicts that the "Deals in Dispute" era is likely to persist. As long as market volatility remains and valuation discrepancies exist between different classes of investors, the incentive for activists to intervene in M&A will remain high.
Conclusion: A New Standard for Board Preparation
The Diligent Market Intelligence and Seward & Kissel report serves as a definitive map of the current M&A battlefield. For U.S.-listed companies, the message is clear: the announcement of a deal is no longer the end of a process, but the beginning of a potential conflict.
To navigate this landscape, boards must prioritize transparency and proactive engagement with their shareholder base. The record-high success rates of activists in 2025 demonstrate that shareholders are more willing than ever to challenge the status quo if they perceive a lack of value or a breach of fiduciary duty. In this environment, the best defense is a well-articulated strategic rationale, a demonstrably independent evaluation process, and a deep understanding of the activist playbook.
As the report concludes, contested M&A is a "durable feature" of the modern market. Companies that fail to prepare for this reality risk not only the failure of their strategic transactions but also a broader loss of investor confidence that can take years to rebuild. The data from 2015 to 2025 provides the evidence; the challenge now lies with corporate leaders to adapt to this increasingly litigious and activist-driven world.
