More than 71 deputies of a total of 126 voiced their support for Karami on Wednesday. The president, a staunch supporter of Syria, was backed by a parliament dominated by Syria's allies.
However, his reappointment on Thursday has dismayed those who had sought an end to Syria's domination in Lebanon, threatening to lock Beirut into a political impasse.
With parliamentary elections scheduled for May, opposition MPs are saying they will refuse to participate in a new government until their demands are met.
Faris Swaid, an MP who is part of a leading opposition grouping known as the Qurnat Shahwan, said three conditions had to be met before there could be a resumption of normal political life in Lebanon.
"The direct aggression that has taken place against the Lebanese people by the assasination of [former prime minister] Rafiq al-Hariri must be opened to an international investigation and quickly," Swaid said in a telephone interview from Beirut on Thursday.
"Second, the Syrian and pro-Syrian Lebanese secret services must be removed from our streets. And, third, a total withdrawal of Syrian troops out of Lebanon must take place before the elections."
Swaid added: "It is unacceptable to replace Karami with Karami, because his government is responsible for allowing all that has happened."
In recent weeks, tens of thousands of Lebanese have demonstrated against Syria following the assassination of al-Hariri on 14 February.
Lebanese society is polarised
along pro- and anti-Syrian lines
The protests led to Karami's resignation on 28 Febuary and forced Syrian President Bashar al-Asad to say he would withdraw his troops from Lebanon, which they first entered in 1976.
Renoud Leenders, an analyst for the thinktank International Crisis Group (ICG) who is based in Beirut, describes Karami's return as "a surprising move given that his resignation was a sign of acknowledging the Lebanese public's will for change" in the wake of al-Hariri's killing.
Speaking to Aljazeera.net on Thursday, he said: "The Syrian and pro-Syrian Lebanese elements obviously feel that the speech by al-Asad [announcing a withdrawal of Syrian troops] and the pro-Syrian mass rally organised by Lebanese Hizb Allah two days ago, have rapidly changed the political atmosphere [enough] to re-appoint Karami."
"It is unacceptable to replace Karami with Karami, because his government is responsible for allowing all that has happened"
opposition Lebanese MP
Pressure from the United States and the European Union has been mounting on Syria to withdraw its 14,000 soldiers from Lebanon since it imposed a three-year extension of Lahud's presidency, an action that prompted the resignation of al-Hariri as prime minister in October and his replacement by Karami.
President George Bush called al-Asad's moving of troops back to the Bekaa Valley in Lebanon a "half measure" that fell short of UN Security Council 1559, which demanded complete withdrawal.
But Damascus, emboldened by the turnout of hundreds of thousands for a pro-Syria rally in Beirut on Tuesday, has reasserted its authority for now.
This is the third time that Karami, a scion of a prominent Sunni family and a Syria loyalist, has been called to head Lebanon's government.
The fortunes of Karami (L) have
been ressurected for now
Twice he has resigned in the face of street protests. His first resignation was in 1992 after unpopular economic reforms.
The decision to renominate him comes as a reflection of the political void among Sunni Muslims left by the death of al-Hariri, political analysts say.
"Karami's re-appointment is a reflection of the growing need for political unity", Nassar Kandil, a pro-Syrian independent MP from Beirut, told Aljazeera.net in a phone interview on Thursday.
"The opposition's demands have been put on the table and they should support him now. Karami has said that he will appoint a government that represents all the people of Lebanon, so they [the opposition] should accept"
He added: "It is unacceptable to ask for the removal of Karami when they [the opposition] failed to come up with a candidate for prime minister".
Significantly, few opposition leaders have spoken out against President Lahud, prefering instead to focus their attacks on Karami.
"It is unacceptable to ask for the removal of Karami when they [the opposition] failed to come up with a candidate for prime minister"
pro-Syrian Lebanese MP
Only Walid Jumblatt, the Druze leader who has emerged as the most prominent voice against Syria, has asked Lahud to step down as well.
The opposition, built around a fragile bloc of members of parliament, including Christians, Druze and Sunni partisans of al-Hariri, will be significantly weaker without continued public mobilisation against Syria's influence in the country.
Summing up the current situation in Beirut, ICG's Leenders said: "It is unlikely the opposition are in much of a position to oust Karami straight away. Unless Karami reconstitutes the old guard into government, he will live to stay on."