Over the past years, knowledge-intensive industries have gained significant importance as economic factor, giving rise to professional service firms (PSFs) such as law firms, accounting firms, or consultancies. Following this development, the research interest especially in the strategies pursued by PSFs has grown substantially. However, past research focused mainly on strategies of established mature PSFs, leaving academics as well as potential entrepreneurs without guidance on what newly founded, entrepreneurial PSFs should pay attention to in order to ensure lasting competitive advantages. Based on an explorative grounded theory analysis of two outstanding commercial law firm spin-offs in Germany, this work advances the research in this field. In addition to a detailed case study report, it offers a comprehensive theoretical framework and argues that PSFs have to employ a set of seven specific entrepreneurial strategies – including for example service delivery, people development, and client acquisition strategies – in order to successfully manage the entrepreneurial phase. In providing examples for the growing PSF industry, the findings on commercial law firm spin-offs also inform entrepreneurship research in other professions.