The Spaniard has made the perfect start to the clay-court season and will aim for a 10th French Open next month after also claiming his 10th title at the Monte Carlo Masters last week.
Nadal won in Barcelona between 2005-2009, 2011-13 and now in the last two years.
The 14-time Grand Slam champion looks like the man to beat in Paris as on the court newly baptised in his name he failed to drop a set all week.
The world number nine even had his only break point of the match in the first game.
More From This Section
The second set was a procession as Thiem's frustration at his inability to break through Nadal's defences saw him consistently fire long.
Thiem held off three break points in his opening service game, but was powerless to stop Nadal thereafter as he won the last five games to seal victory in just over 90 minutes on court.