Marina specializes in Mergers & Acquisitions, financing transactions and corporate law and co-heads the corporate/M&A practice.

Marina is recognized for her practice in leading legal guides, such as Chambers and Partners, Legal 500, Best Lawyers and Leader’s League, and was voted by her peers as Lawyer of the Year in Mergers and Acquisitions in Lausanne in the 2026 Best Lawyers edition. Described as ‘driven, talented, hard-working and responsive’, Marina ‘combines in-depth knowledge of the law and razor-sharp analytical skills with sound commercial judgment and pragmatic solution finding’ (Legal 500/2025). Clients praise ‘her combination of legal acumen, reliability and human approach’ which ‘makes her an invaluable partner and a true pleasure to work with’ (Chambers Europe/2026).

With over 15 years of experience, Marina advises a broad range of clients, including major venture capital and private equity funds, family offices, multinational corporations, startups, SMEs, and seasoned entrepreneurs on various corporate matters, including M&A and distressed M&A, business transfers, venture capital and private equity deals, corporate restructurings, and debt financing. Marina regularly advises on cross-border transactions. Marina also provides legal advice on corporate governance matters, drawing on her extensive professional experience across a wide range of economic sectors.

Before joining id est avocats in 2020, Marina spent over a decade at major Swiss commercial law firms, gaining extensive experience in both advisory and transactional work. She accomplished her legal studies at the Universities of Geneva and Lucerne, and Harvard Law School.

A regular lecturer and published author, Marina contributes to professional publications and has served as the Swiss law expert for several chapters of the World Bank Doing Business Report.

She is licensed to practice before all Swiss courts and works fluently in English, French, and Spanish, with working knowledge of German and Italian.

Selected Recommendations:

· ‘Marina Castelli-Joos is quick at reacting to questions and coming up with answers at meetings, as well as being aware of the market we are in.’ (Chambers Europe/2026)

· ‘Her combination of legal acumen, reliability and human approach makes her an invaluable partner and a true pleasure to work with.’ (Chambers Europe/2026)

· ‘What distinguishes Marina is not only her strong legal expertise but also her remarkable interpersonal skills and emotional intelligence.’ (Chambers Europe/2026)

· ‘I would clearly recommend Marina Castelli-Joos.’ (Chambers Europe/2026)

· ‘I am very pleased with the collaboration with Marina. She is very proactive and understands her clients well.’ (Chambers Europe/2026)

· ‘Marina Castelli-Joos is driven, talented, hard-working and responsive; combines in-depth knowledge of the law and razor-sharp analytical skills with sound commercial judgment and pragmatic solution finding.’ (Legal 500/2025)

· ‘Working close with Marina Castelli-Joos, a great advisor for M&A deals.’ (Legal 500/2025)

· ‘Marina Castelli-Joos is highly qualified and has extensive experience in M&A. In addition, she has great communication skills and is very efficient. She immediately identified the key elements of the deal and assisted us in completing it to our full satisfaction.’ (Legal 500/2024)

· ‘Marina Castelli-Joos is excellent at communicating clearly, always commits to the timeline she outlines and has a very pragmatic, business-oriented approach while focusing on the critical points.’ (Legal 500/2024)

· ‘Marina Castelli-Joos is crazy smart. She thinks about everything. Truly amazed.’ (Legal 500/2023)