Kelly, 44, will succeed 54-year-old Gene Donnelly, who has resigned to pursue other interests, as Apollo CFO no later than October 1, the private equity firm said in a statement. Donnelly will serve as CFO until mid-August and as senior advisor to Apollo until the end of the year, the firm added.

"We are confident that (Kelly's) leadership, finance and accounting experience will benefit Apollo and its employees and investors as we continue to diversify and grow our business on a global scale," Apollo's CEO Leon Black said in a statement.

Kelly worked in several roles at Lehman Brothers and Barclays between 2000 and 2012, including overseeing finance and controls of the equities, investment banking and fixed income businesses. In March 2009, he was made CFO of the Americas and in October 2011 appointed global head of financial control for Barclays' corporate and investment bank.

Barclays has admitted it submitted artificially low estimates of its borrowing costs from late 2007 to May 2009 because it thought rivals were doing the same and higher submissions would make it appear it was in trouble.

From September 2008 to March 2009, Kelly served in a variety of senior finance roles at Barclays, according to a regulatory filing by Apollo. However, there is no suggestion he was involved in the affair.

From 2000 to 2007, Kelly worked on accounting and regulatory matters relating to the corporate and financial institution clients of Lehman Brothers, the bankrupt U.S. investment bank Barclays took over in 2008.

Controllers are primarily accountants responsible for accurate filing and financial reporting and they are usually separate from treasury, where borrowing rates are reported. A Barclays spokeswoman declined to comment on Kelly's responsibilities.

Barclays has been fined more that $450 million for its part in manipulating Libor, the interest rate that is the global benchmark for transactions worth billions of dollars.

Apollo said it entered into a letter of agreement with Kelly about the CFO job on July 2. Barclays' settlements with U.S. and British authorities regarding Libor were announced on June 27. It was not clear for how long Kelly was negotiating a move to Apollo.

PRICEWATERHOUSECOOPERS

Before joining Lehman in 2000, Kelly spent 13 years with accounting firm PricewaterhouseCoopers. He has a degree in commerce, majoring in finance and accounting, from the University of New South Wales.

Donnelly joined Apollo in 2010, following a 30-year career also with PricewaterhouseCoopers, to take the firm public. Apollo raised $565 million in an initial public offering in March 2011.

Donnelly received total compensation of $4.4 million in 2011 which includes a $1 million base salary, shares and other compensation but excludes dividend payments as a result of his Apollo stock ownership.

Kelly's annual base pay will also be $1 million. He will receive a one-time sign-on bonus of $200,000, an annual bonus of no less than $1.89 million for 2012 and an annual bonus of no less than $1.5 million for 2013, Apollo said.

Apollo, whose investments include casino operator Caesars Entertainment Corp, chemicals company LyondellBasell Industries NV and real estate investor Realogy Corp, was founded by Black, Joshua Harris and Marc Rowan in 1990.

The New York-based private equity firm has been diversifying beyond buyouts into areas such as credit and real estate in a drive to make its earnings less volatile and easier for investors to anticipate. Its credit assets have overtaken its buyout assets in size.

(Reporting by Greg Roumeliotis in New York; Additional reporting by Jed Howowitz in New York; Editing by Andre Grenon and Richard Pullin)

By Greg Roumeliotis