Bank of America Merrill Lynch's Andrea Orcel, the architect of many of Europe's biggest banking deals including the break-up of ABN Amro, is leaving to jointly head UBS's investment bank, three people familiar with the matter said.

Orcel's departure is a blow to Bank of America Chief Executive Brian Moynihan, who is under pressure to fix the performance of the U.S's largest lender, and a coup for the Swiss bank which is fighting to restore its fortunes after a $2 billion trading scandal.

Orcel, who was appointed executive chairman of global banking and markets at Bank of America Merrill Lynch (BAML) in September 2009, will join Carsten Kengeter as joint head of the investment bank at UBS, the people said. Kengeter's future at UBS has been widely questioned since the trading scandal last year.

The move will reunite Orcel with Ermotti, who took over at UBS when Oswald Gruebel quit late last year.

Orcel advised Spain's Santander when it bought part of Dutch bank ABN Amro and more recently worked on a 7.5 billion euro ($9.89 billion) equity raising for Unicredit .

Kengeter, a contemporary of Gruebel survived the cull that cost Gruebel his job and also claimed equities co-heads Francois Gouws and Yassine Bouhara.

Ermotti, who worked at Merrill Lynch from 1987 to 2005, is overseeing a return to the Swiss bank's roots, the comparatively conservative and stable-profit businesses related to private banking.

"Sergio knows Orcel very well, it is normal for a new chief executive to want to bring in people he is close to and has worked with before," one of the people said. "This is a great hire. Orcel is a relationship man, not a manager."

It is likely that corporate finance bosses Simon Warshaw and Matthew Grounds will report into Orcel as well as Kengeter when he joins the bank.

"Carsten has a trading background and Andrea is focused on relationships with clients, there should be a natural fit," a second person said.

Orcel, once touted as a contender to lead Italy's UniCredit, comes from a family of high-flying investment bankers and has caused controversy in the past on account of his salary.

At the height of the crisis in 2008, he received close to $34 million in stock and cash from Merrill Lynch for his services.

Brother Riccardo Orcel was a top executive at BAML until last year, when he left a job running investment banking for central and eastern Europe, the Middle East and Africa to join Russia's second biggest lender VTB .

Bank of America has raided UBS for some big hires when it was vulnerable, poaching equities and Asia specialist Matthew Koder last year.

But Moynihan is under pressure from investors to improve performance after the bank lost money in four of the last six quarters and its stock had fallen by half this year.

A BAML insider said it was not surprising to see senior people leaving as the restructuring is enacted.

"Andrea is a very key person so it's not great for us," the person said.

BAML and UBS declined to comment.

Orcel was not available for immediate comment. ($1= 0.7582 euros)

(Additional reporting by Sarah White in London and Katharina Bart in Zurich; Editing by Steve Slater and Elaine Hardcastle)