Definely elevates AI leader to CTO

London-based legaltech company Definely has appointed Sigurjón Ísaksson as chief technology officer, strengthening its senior leadership team following a period of rapid growth.

Sigurjón steps into the role after joining Definely in 2024 as head of AI, where he led the development of key products that expanded the company’s AI capabilities and agent architecture. 

His promotion follows a landmark year for the business, including a $30 million Series B funding round and expansion into North America.

He brings nearly ten years’ experience as a machine learning engineer, alongside previous experience as CTO and co-founder of fintech business Nosso.

In his new role, Sigurjón will continue to lead Definely’s product development and oversee the scaling of its technical and AI engineering teams.

He said: “2025 has shown that Definely’s AI offering is uniquely positioned within a crowded market, and the customer success speaks for itself. 

“I have spent the last two years developing first-of-its-kind AI solutions for complex contract reviewing, unifying Definely’s existing product stack to solve end-to-end workflows for lawyers, and I look forward to doubling down on this as chief technology officer. 

“I am excited to lead an incredible tech team and push the boundaries of deep AI innovation we have achieved in 2025.”

Definely is an AI-powered legaltech business that helps lawyers review complex contracts by integrating directly within Microsoft Word.

Nnamdi Emelifeonwu, co-founder and chief executive of Definely, added: “Sjonni has already proven what he can do at Definely. 

“As head of AI, he led the development and launch of Enhance and Cascade, products now trusted by law firms and in-house legal teams around the world. 

“Appointing him as chief technology officer gives us continuity and real momentum: faster shipping, stronger technical ownership across both AI and platform, and a clear focus on scaling reliability, security, and enterprise readiness as demand accelerates. 

“Just as importantly, Sjonni is building the kind of high-performing engineering organisation that will help us deliver consistently as we grow.”

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