Pimco said it had formed a five-strong group of "world-renowned experts on economic and political issues".
The other members include former US Federal Reserve chairman Ben Bernanke, and Jean-Claude Trichet, former president of the European Central Bank.
A spokesman for Mr Brown said he was taking on "a minor advisory role" and would not financially benefit.
The spokesman added: "Any money goes to the office of Gordon and Sarah Brown to support their charitable and public service work."
The advisory board will meet several times a year.
"The global advisory board is an unrivalled team of macroeconomic thinkers and former policymakers, whose insights into the intersection of policy and financial markets will be a valuable input to our investment process," Dan Ivascyn, Pimco's chief investment officer, said.
The other members are Ng Kok Song, former chief investment officer of the Government of Singapore Investment Corp sovereign wealth fund from 2007 to 2013, and Anne-Marie Slaughter, a former US Department of State policy director.
Pimco, which was bought by German asset manager Allianz in 2000, administers about $1.47 trillion of assets for its clients.
This hiring flurry follows last year's departures of co-chief investment officers Bill Gross and Mohamed El-Erian.
Former Prime Minister Gordon Brown has taken up a role on an advisory panel at a global investment management firm.