Democratic presidential candidate Barack Obama has picked former rival Joe Biden to be his running mate.

Obama had kept his pick a closely-guarded secret, and had promised to reveal it in a mass text message to supporters on Saturday morning, but Democratic Party sources leaked Biden’s name to journalists in the early morning hours.

65-year-old Biden, a six-term Democratic Senator from Delaware, had emerged as
the front-runner.

The field of candidates included Virginia governor Tim Kaine, New Mexico governor Bill Richardson, Kansas governor Kathleen Sebelius, India Senator Evan Bayh and New York Senator Hillary Rodham Clinton.

Obama is scheduled to introduce his running mate on Saturday afternoon at a rally in Springfield, Illinois. Biden will make his first big speech as the vice-presidential candidate in Denver on August 27, the third night of the Democratic National Convention, at which Hillary and Bill Clinton are also scheduled to speak.

Obama said he had finalised his running mate selection, but refused to reveal who it was. The suspense built over the next 24 hours and the choice became clearer on Friday night as Kaine and Bayh said they had not been picked. ABC News reported that the Secret service had dispatched a team to protect Biden.

On CBS's Early show, Obama said, “I want somebody who is going to be able to challenge my thinking and not simply be yes-person when it comes to policymaking.”

By picking Biden, Obama has tapped a candidate with a weighty foreign policy resume. Biden is the chairman of the influential Senate Foreign Relations Committee.

With Biden on his ticket, Obama can more easily fend off Republican critics who have attacked him over his shallow foreign policy experience.

Among other foreign policy issues, Biden is well-versed in South Asian affairs and is known to the leaders of nations in the region.

Jonah Blank, a top Biden staffer, has for a while been working with the Obama campaign as an adviser on South Asia. During the primaries, Biden had pointed to Pakistan as a growing source of instability.

This was well before the assassination of former prime minister Benazir Bhutto and the resignation of president Pervez Musharraf.

Soon after Musharraf announced his resignation this month, Biden urged Pakistan’s leaders to focus now on the pressing challenges of the future Biden has been an ardent supporter of a strong US-India relationship.

One of the key leaders in the Senate, he helped push the US-Indo nuclear agreement over the hurdles in the Congress.

In a 2006 incident that angered Indian- Americans, Biden said, “In Delaware, the
largest growth in population is Indian-Americans moving from India. You cannot
go to a 7-Eleven or a Dunkin’ Donuts unless you have a slight Indian accent. I’m
not joking.”