MADRID (AFP) - Spain's former Socialist chief Pedro Sanchez, who was ousted in a party rebellion this month, said Saturday (Oct 29) he had quit as lawmaker just hours before his conservative rival is voted back in power.

"I am appearing here in this press room to announce my resignation as MP," the 44-year-old said in an emotional declaration during which he emphasised "how painful the decision was" before breaking down and choking back tears.

But he maintained he was not quitting politics altogether, leaving his options open for an upcoming leadership contest that promises to be acrimonious as the Socialist party remains in disarray.

At the head of the Socialists since July 2014 when he won the first ever primaries organised by the party, Sanchez was a staunch opponent of conservative Prime Minister Mariano Rajoy, blasting the corruption scandals and spending cuts that marked his first term.

Throughout Spain's protracted political crisis, which saw parties unable to reach any viable coalition deal following two inconclusive elections, he steadfastly refused to back Rajoy's Popular Party, which came first in both polls but without enough seats to govern alone.

But as election-weary Spain faced the prospect of yet more polls, the Socialists grew divided among those who wanted to break the deadlock and let Rajoy rule, and others like Sanchez who refused.

Sanchez eventually lost the fight and was forced out on Oct 1.

With him out of the way, the Socialists opted to abstain in a crux parliamentary confidence vote due later Saturday, which will give Rajoy enough traction to see him through and once again lead Spain, if at the head of a minority government.

As a lawmaker, Sanchez had the choice between going against his principles and abstaining, or going against his party and voting no to Rajoy. So he opted out entirely.

"I am convinced that the majority of voters and militants don't elect the Socialist party to then support what they want to change," he told reporters.

"Spain needs a credible alternative to the Popular Party's policies," he said, adding he believed Rajoy's new government would be more of the same.

From Monday, he said, the Socialists' interim executive should set a date and place for an extraordinary congress to re-elect a party chief.

And while he remained mum on whether he would present himself again, he stressed he would be attending the primaries.