Holcomb and Langton had trailed Canada's Lyndon Rush and Jesse Lumsden after the first two runs on Saturday, but came through in the third run on Sunday to take the gold medal in an aggregate time of three minutes 42.88 seconds, 0.46 seconds ahead of Rush and Lumsden.
Germany's Maximilian Arndt and Kevin Kuske took the bronze, just 0.09 further back.
Holcomb's win was the first ever in the two-man World Championships by an American, and the driver was thrilled.
"That's going to take a little while to sink in," said Holcomb. "My world championship medal it had been 50 years (since an American won). My (Olympic) gold medal was 62 years. And now this -- never, ever. This is no years. It's going to take a little bit to sink in."
The Canadians' disappointment was tempered by the fact that Rush was hampered by a virus which struck him and hurt his chances.
"Coming down the track was awful. I was gagging the whole way down. Thankfully the run is only a minute long," said Rush. "Jesse pushed the sled by himself today. I was basically a windsock. He was on his own."
Lumsden paid tribute to his team-mate.
"Considering the condition Lyndon was in it was a courageous effort even for him to perform. We gave it everything we had and Team Rush are world championship medallists."