An initial accord ending more than 50 years of conflict was struck in late September, but rejected by Colombians in a vote.
Days later Mr Santos was awarded the Nobel Peace Prize, which he said gave a "tremendous push" for a new deal.
He is in the Norwegian capital Oslo and will collect the prize on Saturday.
None of his co-signatories from the Farc are attending, with the group still designated as a terrorist organisation in many countries.
Mr Santos said, however, that they "will be here in heart and spirit".
On his award, he said: "It came like a gift from heaven, because it gave us a tremendous push.
"People in Colombia interpreted it as a mandate from the international community to persevere, to continue striving to achieve a new peace agreement."
The Colombian government and the Farc signed a revised deal in November.
The conflict has killed more than 260,000 people and left millions internally displaced.
Colombian President Juan Manuel Santos has said his Nobel Peace Prize came "like a gift from heaven" in his bid to forge an agreement with Farc rebels.