"I am confident personally that the Syrian opposition will come to Geneva," Kerry said after a meeting of the 11-nation "Friends of Syria" group that was attended by Coalition leader Ahmad Jarba.
The bloc is under intense pressure to confirm its participation in the talks, scheduled to begin on January 22, and has said it will decide on the issue next Friday.
The Friends of Syria, an alliance of mainly Western and Persian Gulf Arab countries who support the opposition, earlier on Sunday stated that the conference, bringing Syrian government's negotiators and opposition groups together, is necessary to solve the crisis.
"There is no other political solution," French Foreign Minister Laurent Fabius said, speaking on behalf of the group. "There will be no political solution for Syria unless Geneva 2 meets."
Kerry reiterated that there is "no military solution" to the conflict, which has killed more than 120,000 people, Al Jazeera reported.
In a joint statement, the Friends of Syria nations - US, Britain, France, Germany, Italy, Turkey, Saudi Arabia, the United Arab Emirates, Qatar, Egypt and Jordan - urged the Coalition to attend the upcoming talks.