Reigning champion Medvedev cruised through to the final after wrapping up a 6-4 6-2 win in one hour and 20 minutes in Turin.
The world No.2 is aiming to become the ninth different player to successfully defend this title.
Medvedev reached the semi-finals of the year-ending championship with a match to spare, winning three out of three in the Red Group, and did not offer up a single break point against Ruud, who he had beaten in both of their previous meetings.
The US Open champion took early command, breaking in game three and holding before serving to love to take the opening set.
The winner of five ATP Tour titles in 2021, world No.8 Ruud was aiming to become the third debutant to lift this trophy in five years after Grigor Dimitrov (2017) and Stefanos Tsitsipas (2019).
However the Norwegian, who squeezed past Andrey Rublev on Saturday (AEDT), was broken twice in the second set as Medvedev surged into a 5-2 lead, before serving out to complete a ninth straight win at this event.