NEW YORK – Barack Obama, the presidential candidate Keith Olbermann championed this fall, just won a four-year term. So, too, has Olbermann.

MSNBC announced Monday that Olbermann, its headlining prime-time star, has signed on to continue hosting “Countdown” each weeknight at 8 o’clock EST. MSNBC essentially tore up an existing contract Olbermann had, adding a year and a half and more money. (Exact terms of the deal were not disclosed.)

It’s also four more years of cable television’s most sizzling rivalry. Fox News Channel said last month that Bill O’Reilly, whose show airs opposite Olbermann’s, had also agreed to a new four-year contract.

Olbermann’s fans made him a folk hero during the campaign for his sharp-tongued criticism of John McCain and President Bush. The size of his audience has more than doubled, from an average of 776,000 in October 2007 to nearly 2.2 million this October, according to Nielsen Media Research. O’Reilly’s audience hovered around 4 million a night in October 2008. (But the two were much more competitive among the 25-to-54 age demographic; Olbermann beat his rival seven nights in October in that category.)

MSNBC has built its prime time in Olbermann’s image, hiring Rachel Maddow – a frequent Olbermann guest – for a successful 9 p.m. show. (Olbermann’s telecast is repeated each weeknight at 10.)

MSNBC said Olbermann will continue to play a major role in coverage of big news events. MSNBC installed him as a co-anchor with Chris Matthews during the primary campaign, but later switched him to a commentator role.