Steinmeier, currently vice chancellor and foreign minister in the coalition government, will be the party's chancellor candidate, putting him directly up against Chancellor Angela Merkel for Germany's top political job.
Müntefering will return to the job of party chairman, completing a change of guard in the SPD, with friends and close colleagues of former chancellor Gerhard Schröder once again taking charge.
The SPD has been forced to hold this extraordinary meeting by the resignation of former party chairman Kurt Beck who failed to pull the left and centrist wings of the party together and then felt the target of a campaign to oust him.
Berlin mayor Klaus Wowereit said he was hoping the meeting would mark the beginning of unity in the party, unity which is sorely needed as it bumps along the bottom of polling data, dropping recently from 27 to 24 percent.
Müntefering and Steinmeier will have to carry the more left-wing members of the party with them, members which had been turned off by the Schröder leadership and had worked to kick Müntefering off the party chairman throne in 2005.
Andrea Nahles, the woman considered to have engineered that blow, was scheduled to speak first at Saturday's meeting, a sign that the party managers are keen to draw all sides together.
Hubertus Heil, SPD secretary general said the global financial crisis was bringing people to the social democratic way of thinking.
“Trades unions and even business are showing new interest in a dialogue with us,” he told Die Welt newspaper. “We are more self-confident again.”