The newly created role was announced by Daniel Ivascyn, Pimco's group chief investment officer, to whom Seidner will report.

Seidner, who was a senior portfolio manager at Pimco from 2009 to 2014, resigned just hours before Pimco stunned the asset management world last January by announcing the departure of former Chief Executive Mohamed El-Erian, the result of a falling out over Gross's leadership style and investment strategy.

Long considered to be in line to succeed Gross as the firm's top investment executive, El-Erian was also a close confidant of Seidner.

Seidner, who left Pimco to become head of fixed income at Boston-based money management firm Grantham Mayo Otterloo & Co (GMO), had turned down an offer to become one of Gross' top lieutenants.

Newport Beach, Calif.-based Pimco oversees $1.87 trillion (1.17 trillion pounds) as part of German insurer Allianz SE. It said Seidner also will be the head of portfolio management in Pimco's New York office, as well as a member of Pimco's Investment Committee. He will start on Nov. 12.

"I look forward to returning to Pimco and becoming a member of the firm's portfolio management team, which is one of the deepest in the investment management industry," Seidner said in a statement. He added: "This new role provides me a unique opportunity to again contribute to Pimco's success while also enabling my family and me to remain based on the East Coast."

(Reporting by Jennifer Ablan; Editing by Dan Grebler)

By Jennifer Ablan