Rawlinson, who has been at law firm Freshfields since joining in 1982, will join in October, Morgan Stanley said.
He was head of corporate at Freshfields from 2008 to 2011, and head of London from 2011 to 2013.
The US bank said Rawlinson had been a leading adviser on some of the UK's biggest deals, including AB InBev's takeover of SABMiller, which Morgan Stanley also worked on. He also advised BP on its Gulf of Mexico oil spill crisis that started in 2010.