The US Secret Service is to pay dozens of African-American former agents $24 million in settlement of a class-action lawsuit alleging racial discrimination.

This marks the end of 16 years of contentious litigation which began in the year 2000 when over 100 black Secret Service agents alleged that they were routinely passed over for promotions in favour of less-qualified white agents.

Eight of the 10 original claimants could receive up to $300,000 in settlement funds.

Homeland Security Secretary Jeh Johnson said in a statement released on Tuesday night that he is "pleased that we are able to finally put this chapter of Secret Service history behind us."

As part of the agreement, the Secret Service admitted no wrongdoing that while it "denies any and all liability or damages the agreement is a means of resolving this almost 2-decades-old matter."

According to NBC News, court documents show some of the claimants applied for promotion over 100 times without success.

Special Agent Reginald G. "Ray" Moore was said to have applied for promotion 180 times without success, despite that he was competent enough to be tasked with protecting President Bill Clinton.

The suit also states that at one point Moore was asked to train a white selectee for a position on which he had previously applied for.

Other original plaintiffs said they were passed over for promotions for which they were qualified as many as 160 times.

The lawsuit also alleged that white agents and supervisors regularly used the "N" word to refer to suspects and black leaders of other countries.