The pontiff had been one of the favourite for the award after his interventions in the relationship between Cuba and the USA and for his opposition to nuclear weapons.
The prize, however, went to The National Dialogue Quartet in Tunisia.
The jury cited the group for "its decisive contribution to the building of a pluralistic democracy in Tunisia in the wake of the Jasmine Revolution of 2011".
Nobel committee chairwoman Kaci Kullmann Five said: "More than anything, the prize is intended as an encouragement to the Tunisian people, who despite major challenges have laid the groundwork for a national fraternity which the committee hopes will serve as an example to be followed by other countries."
There were 273 candidates nominated for the 2015 peace prize, made up of organisations and individuals.
German Chancellor Angela Merkel was also one of the favourite along with Father Mussie Zerai, an Eritrean priest who founded a humanitarian organisation for refugees.