A&O Shearman loses head of German arbitration as Anna Masser launches Hamburg boutique with Simon Manner

The new firm of Anna Masser and Dr. Simon Manner, to be launched in October, will operate under the name Manner Masser, immediately positioning itself as a dedicated disputes powerhouse in one of Germany’s most competitive legal markets.

For A&O Shearman, the departure marks a significant turning point. Masser was instrumental in rebuilding the firm’s German arbitration practice following the high-profile departure of a large team in 2019. Over the past five years, she stabilized the practice and reasserted its presence in major commercial and investment treaty disputes. Her leadership was seen internally as a critical asset during the merger negotiations between Allen & Overy and Shearman & Sterling, which culminated earlier this year.

Anna Masser brings an unusual blend of international experience and local market insight. Before joining A&O, she built her reputation across several leading international firms and has acted in proceedings under the rules of major arbitral institutions, including the ICC, DIS, SIAC and ICSID. Known for her strategic thinking and ability to navigate complex cross-border disputes, she is frequently appointed as arbitrator herself, a testament to her standing in the arbitration community.

Her new partner, Dr. Simon Manner, is equally well established. Based in Hamburg, he has been advising clients for two decades on commercial arbitration, litigation and alternative dispute resolution. Manner is recognized for his expertise in corporate disputes, energy sector matters, and post-M&A arbitrations. His combination with Masser creates a formidable pairing: two senior practitioners with complementary backgrounds, united by the ambition to build a boutique that is both international in outlook and agile in structure.

The emergence of Manner Masser highlights a growing trend in the German legal market: the increasing appeal of specialist disputes boutiques as alternatives to large, full-service firms. Clients in high-stakes arbitration often value the independence, focus and cost flexibility that boutiques can offer, without sacrificing international credibility. In this sense, Masser and Manner are following a path successfully taken by other leading arbitration practitioners across Europe, who have carved out influential positions by stepping away from the big-law environment.

Both Masser and Manner have cultivated strong relationships with German corporates as well as international investors, and their new venture is expected to attract mandates quickly.

For A&O Shearman, the timing is challenging. The combined firm is in the midst of consolidating its global disputes offering, seeking to leverage Shearman’s historical strength in New York and Allen & Overy’s broad international network. IWhile A&O Shearman retains a substantial disputes bench across Europe, the loss of a practice head with Masser’s profile underscores the competitive pressures facing global firms as they integrate, merge and seek to retain top talent.

Ultimately, the launch of Manner Masser represents both continuity and change. Continuity, in that it reinforces Hamburg’s status as a hub for arbitration in Germany; change, in that it signals the growing maturity of the boutique model in a market long dominated by international full-service firms. For Masser and Manner, it is an entrepreneurial step that aligns with broader shifts in client demand. For A&O Shearman, it is a reminder that even as the firm achieves historic consolidation, talent mobility continues to shape the competitive landscape.

Sophie Stevenard