The victory was already established in the first set where Nadal broke Ruud's first two serve games.
When the 23-year-old final debutant did not manage to return to the match despite a 3-1 lead in the second set, Nadal walked away and won in three straight sets.
In the final set, Nadal was superior and did not lose a game.
The title was the Spaniard's 14th French Open.
Since playing in the tournament for the first time in 2005, the 35-year-old has only lost three matches.
Nadal has now won the two grand slams played this year (Australian Open and French Open) and has the chance to become the first male player in history to take a "true grand slam", to win all four tournaments (Wimbledon & US Open) the same year.
However, it is not clear if he will participate in the two recurring tournaments.
Wimledon starts in three weeks.