The former Wales skipper was appointed as the leader of the Lions ahead of their tour of Australia in the summer, with his good relations with South African official Craig Joubert, who will referee the second Lions Test against Australia in Melbourne on June 29, playing a part in the decision.
Gatland says that he was impressed by the way that the 24-year-old spoke to the official during Wales' Six Nations decider with England when he was not even captain.
"There are only two or three players in the world that referees would allow to [talk to them]," Gatland told Sky Sports News. "It's the ability Sam has to communicate with referees and when I saw that against England it really stuck in my mind that this guy could do a job for us and potentially have a positive influence on the game with his relationship with referees.
"I think Craig has got a really good relationship with Sam. Having spoken to Craig I know that he regards Sam as one of the best sevens in the world. He regards him on a par with [Richie] McCaw and [David] Pocock in terms of the way he is at the breakdown, his physicality and the way he carries.
"So when a referee makes these comments to you in terms of enjoying his leadership and saying that he's got a good rapport with him, it makes it a kind of easy decision for me to make in terms of appointing him as captain."
The Lions will play 10 matches down under in the summer, including three Test matches.