McDonnell was a senior financial planning specialist at Coutts and will be reunited with Liz Bottomley, who Arbuthnot Latham poached from Coutts last week as its new head of private banking.
A busy few days for Arbuthnot has also seen the recruitment of Linda Amili Clack as international banking director and head of Middle East private banking.
McDonnell will work under another recent recruit, chief executive James Fleming, and alongside both the private banking and investment teams.
Arbuthnot Latham claims to be the only private bank currently to hold chartered status. Ian Scott, head of wealth planning, spoke of the firm’s determination to build a wealth planning unit based on the “highest level of wealth planners in the industry”.