"The Fed does not regulate Pimco or its parent or any other firm that is affiliated with it," Bernanke said. The same situation obtains with Citadel, he said. "So there is no contact."

He added: "I am not going to be involved in any kind of lobbying or any kind of influence with the Fed or Congress or anybody else in the government."

Former Fed chairman Alan Greenspan, Bernanke's predecessor, also consulted for Pimco, which is owned by Germany's Allianz SE , between 2007 and 2011.

In late 2008, the Fed hired Pimco, along with three other big Wall Street firms, to implement enormous purchases of agency mortgage-backed securities to keep interest rates low and spur the U.S. economy. Pimco also managed the commercial-paper assets for the Fed during that period.

"If they were employed to do that kind of thing, that was in their professional capacity," Bernanke said. "I had nothing to do with selecting them or I had no involvement with them myself."

When asked if he has advised Pimco to prepare for an expected interest rate hike this year, Bernanke said: "No, I haven't given them any advice on that. I will be speaking broadly about the economy and markets."

All told, Bernanke said: "From my perspective, they are a firm that the way they operate is by taking a macro view -- they try and decide how they see the economy evolving both in the United States and abroad and they base their investment strategies on that macro view. That's something where I believe I can be helpful, thinking about where the economy is going."

Bernanke, who was a guest speaker at a Pimco client event in mid-March and a participant at the firm's year-end investment forum last December, said discussions about joining Pimco began in October.

Bernanke's lawyers, Robert Barnett and Michael O'Connor of Williams & Connolly LLP, were the chief architects of the Pimco arrangement, according to a source familiar with the matter. Barnett and O'Connor are said to also have brokered Greenspan's advisory deal with Pimco, the source added.

Bernanke's appointment comes as investors continue to pull money from some Pimco funds six months after the exit of Gross. Pimco has seen $123.5 billion of net withdrawals from its open-ended funds since Gross' departure even as performance has improved.

Outflows from the flagship Pimco Total Return Fund, the world's largest bond fund which Gross managed since 1987, have slowed to an average of $7 billion to $8 billion a month recently from $23.5 billion in September.

In the first three months of the year, the Pimco Total Return Fund delivered a net after-fee return of 2.22 percent, outperforming its benchmark by 61 basis points and generating excess returns of 68 basis points above the Morningstar Intermediate Term Bond Average.

"We are honored to have Dr. Bernanke serve as an advisor to Pimco, and look forward to benefiting from his extraordinary knowledge and expertise to help us add value for our clients," Douglas Hodge, Pimco's chief executive officer said in a statement.