In the 1976 presidential campaign, he helped manage the convention floor for Ford, and later worked for the campaigns of Ronald Reagan, George H.W. Bush and Bob Dole.
Manafort was also a senior advisor to Viktor F. Yanukovych, the pro-Russian president of Ukraine from 2010 until he was driven from power in 2014. One of the indictment counts says that from about 2008 to 2014, Manafort and Gates acted as foreign agents without registering, as the law requires.
Those connections to Russia have attracted the most scrutiny as the Trump administration grapples with the investigation by special counsel Robert Mueller into possible Russian influence on the presidential election.
Manafort joined Donald Trump's campaign for president in March 2016 and rose to campaign chairman that June.
On Aug. 14, 2016, The New York Times, citing Ukraine's National Anti-Corruption Bureau, reported that secret, handwritten records show $12.7 million in undisclosed cash payments designated for Manafort from Yanukovych's political party from 2007 to 2012. Manafort's lawyer denied to the Times that Manafort had received the payments.
Three days later, Manafort was effectively demoted when Trump named Breitbart News head Steve Bannon as campaign chief executive officer and promoted Kellyanne Conway to campaign manager.
Manafort resigned on Aug. 19.
According to an April 4 transcript of a CNN interview, Manafort said, "As far as the Yanukovych administration is concerned, you will see if you do any fact checking that I was the person that negotiated the framework, which is based upon which Ukraine is now a part of Europe. That was my role. That's what I did. And when it was completed, I left."
In September, The Washington Post, citing sources, reported that Manafort offered to brief a Russian billionaire with Kremlin ties about the 2016 presidential campaign. Earlier this year, news reports revealed that Manafort also attended a June 2016 meeting with a Russian lawyer at Trump Tower at which Trump's son Donald Trump Jr. and son-in-law, Jared Kushner, were also present.
— CNBC's Christine Wang and Reuters contributed to this report.