Stagwell will invest in MDC through the purchase of $50m in common shares and $50m in non-voting convertible preference shares.

The move concludes a strategic review and chief executive search begun by MDC in September.

As chief executive, Penn (pictured) will lead day-to-day operations at MDC. He also joins the board of directors. Following the transaction, he will continue to oversee investments at The Stagwell Media LP fund.

Prior to founding Stagwell Group, Penn held senior executive positions at Microsoft, working across the company’s products, value propositions and investments and leading competitive research and analysis.

Irwin Simon, presiding director of the MDC Partners board of directors, said: “We are delighted to welcome both Mark as chief executive of MDC Partners, and The Stagwell Group as a long-term strategic investor. Throughout his career, Mark has proven himself a powerful strategic operator and passionate supporter of agencies. He shares our vision and our values, and his background will be critical to bolstering our structure, solutions and services.”

Simon added that the investment would allow the company to “selectively invest behind our world-class talent” and focus on “high-priority growth areas”.

Stagwell Group’s portfolio of companies includes research firm Harris Insights & Analytics, telecoms researcher HarrisX,  entertainment research firm National Research Group (NRG) and performance marketing agency Forward3D.