Stiller, who has worked with both stars, told reporters that he thinks that it is wonderful that Aniston and Theroux have found each other.
"They seem to be really happy together. They're both great people. I love them both," the Tower Heist actor revealed to Us Weekly.
Stiller's spouse Taylor praised Aniston and Theroux as a wonderful couple, saying: "They're both just very cool, terrific people."
Theroux and Aniston went on their first vacation together in August to attend Stiller's birthday party on the Hawaiian island of Kauai.
Earlier this week, Aniston laughed off rumours that she and Theroux are engaged by saying: "I've been married once, and I don't know if I'll get married again. But I can tell you that as of this very moment, I have no plan to get married."
Theroux and Aniston will star together in the upcoming comedy Wanderlust, which opens on February 24, 2012 in the US.
> Justin Theroux ex wants him and Jennifer Aniston out of New York City?
> Barbra Streisand, Jennifer Aniston honoured at Elle tribute: Pictures