Washington: Presumptive Democratic nominee Joe Biden has announced California Senator Kamala Harris as his running mate, ending weeks of increasingly frenzied speculation.

Joe Biden and Kamala Harris shake hands after a Democratic presidential primary debate in September last year.Credit:AP.

Biden said he had gotten to know Harris well during her time working alongside his late son Beau, who served as Delaware's attorney-general.

Presumptive Democratic presidential nominee Joe Biden speaks with his running mate Senator Kamala Harris.

Former vice president and presidential nominee Al Gore who described Harris as "an extraordinary running mate".

Despite being personally upset by the attack at the time, Biden later said that he did not hold a grudge against Harris.

Biden announced at a Democratic debate in March that he would select a woman as his running mate, the first time a candidate has made such an explicit pledge.

Given Biden will be 78 years old by inauguration day, there is a high likelihood he will only serve one term as president - putting his running mate in a strong position to succeed him in 2024