Santos has promised to revive the peace plan even though Colombians, in a referendum on Sunday, narrowly rejected the accord. Many voters believed it was too lenient on the FARC guerrillas.
"The award should also be seen as a tribute to the Colombian people," committee leader Kaci Kullmann Five said when announcing the prize.
Voters did not say "No" to peace but to the agreement, she said.
The award pointedly excluded FARC guerrilla leader Rodrigo Londono, better known by his nom de guerre Timochenko, who signed the deal with Santos.
Some Nobel watchers had taken Colombia off their lists of favourites after the referendum "No".
"The fact that a majority of the voters said "No" to the peace accord does not necessarily mean that the peace process is dead," the committee said.
"This makes it even more important that the parties, headed by President Santos and FARC guerrilla leader Rodrigo Londoño, continue to respect the ceasefire," the committee said.
The Nobel Peace Prize, worth 8 million Swedish crowns ($930,000), will be presented in Oslo on Dec. 10. (US$1 = 8.5891 Swedish crowns)
