Sieda was chosen as the only candidate of the Turkish-based group during a meeting in Istanbul on Saturday.
The selection came although the majority of Syrians are Arabs and Kurds only make up less than ten percent of the population.
Sieda replaced Burhan Ghalioun who resigned following a series of deepening rifts inside the council, which has been criticized repeatedly over internal conflicts.
Sieda said the group supports the so-called Free Syrian Army in its fight against the government of President Bashar al-Assad.
He said on Assad's regime was on its "last legs," even as Russia warned it would block any move at the UN to use force against its ally. "We are entering a sensitive phase. The regime is on its last legs," Sieda told AFP shortly after he was named. "The multiplying massacres and shellings show that it is struggling," he added.
Asked about his ambitions as SNC leader, Sayda said the so-called opposition bloc "would focus its efforts on the international community to take a decisive move against the regime." "We want to strengthen links with activists on the ground and the (rebel) Free Syrian Army, who we will support with all our means", he said.
"The Annan plan still exists but it has not been implemented," he added. "We will work for this plan to be included under Chapter VII of the UN Charter, to force the regime to implement it and to leave all options open," he said.
Syrian opposition elects new leader
Sayda, who has been living in exile in Sweden for many years, was the only candidate for the three-month presidency of the SNC at a meeting of 33 members of the councils' general secretariat.
The 56-year-old succeeds Burhan Ghalioun, a liberal opposition figure who had presided over the council since it was formed in August of last year.
Ghalioun, another exile living in Paris, has come under criticism for having had his presidency constantly renewed when the council was supposed to represent a democratic alternative to the authoritarian rule of President Bashar Assad.
He was further criticized when the details of his personal emails were hacked by pro-regime forces, and revealed his close relationship with both America and Gulf monarchies such as Qatar.
The Muslim Brotherhood, the most influential player in the council, had initially indicated it wanted Ghalioun to remain president, but then opted to support Sayda after opposition activists inside Syria raised objections to Ghalioun following a third renewal of his term last month.
Adib al-Shihakly, a founding member of the council, had also threatened to resign if Ghalioun remained president.
Opposition sources said the election of Sayda could help enlist more Kurds, who number one million out of Syria's 21 million population, behind the 15-month uprising.
Demonstrations against Assad's rule have been regularly breaking out in Kurdish regions of Syria but without matching the intensity of protests in the rest of the country.
That may be partly because of support by Assad for the armed Kurdistan Workers Party (PKK), which is suspected of being behind assassinations of several anti-Assad Kurdish opposition figures.
Kurdish members of the council have also had open disputes with the remainder of the body over the issue of Kurdish rights and whether a post-Assad Syria would be built around a federal structure similar to that in neighboring Iraq.
Sayda said his priority would be to expand the council and hold talks with other opposition figures to include them in the council, which some have accused of being dominated by Islamists.
"The main task now is to reform the council and re-structure it," he said.
Bassam Ishak, a member of the general secretariat, said Sayda was elected to fulfill demands from within the council and from the opposition inside Syria as well as international powers to make the council more democratic.
Sayda will work on convening a meeting of the whole council after a month, during which a new general secretariat and a new president could be elected, possibly making Sayda a transitional leader, Ishak said.
The SNC has struggled to unify a fragmented opposition to President Assad, with many activists inside Syria condemning the group for encouraging foreign intervention.
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