"This is a courageous and historic step in the interest of a negotiated political solution to a three-year conflict that has caused so much misery and destruction," Ban said in a statement.
"I look forward to the opposition's expedited formation of a delegation that broadly represents the diversity of the Syrian opposition, including women," added the UN leader, who is the convenor of the conference that will start in the Swiss town of Montreux on Wednesday.
In welcoming the vote, Ban highlighted that the aim of the conference is "to reach agreement between the Syrian sides on the full implementation of the Geneva Communique of June 30, 2012 and to achieve a political transition that would bring to an end the suffering of the Syrian people."
The major powers and key Middle East nations met in Geneva in June 2012 to agree on a statement which said that there should be a transitional government in Syria with full executive powers.