Shareholder activism is on the rise in Europe. For one Monaco investor, it is paying off.

Activist investor Knight Vinke Asset Management, boosted by a stake in a French electronics company that was engaged in a bidding war, posted a third-quarter return of 14.8% in its flagship fund. This took year-to-date returns to 49.6.%, according to an investor letter seen by The Wall Street Journal. The firm, under founder Eric Knight, manages around $1 billion according to the latest figures.