For almost a decade, Morgan Stanley banker Bernard Mourad guided his client Patrick Drahi, the French telecoms entrepreneur, during fraught negotiations over multibillion-dollar deals. Then, he decided to take a job working for him.

The Lebanese-born financier formally handed in his notice at the Wall Street bank earlier this month to take up the role of executive chairman at Altice Media Group, owned by Drahi. In doing so, he became one of a growing number of investment bankers to switch track, swapping Wall Street for the C-Suite.