Jacobs powered to a shock victory with a time of 9.80 seconds, after qualifying for the final by setting a new European record of 9.84 seconds.
The race, which featured a new generation of sprinters, was the first without three-time champion Usain Bolt since the Athens 2004 Olympics.
Jacobs, 26, was viewed as a surprise contender in the race, which saw American Fred Kerley take the silver medal and Canadian Andre de Grasse win bronze.
The world record for the race was set by Bolt, who retired after the 2017 world championships, with a time of 9.58 seconds.
Having struggled for a long time to even break the 10-second barrier, Jacobs is now the fastest man in the world and just the latest story of Italian success this summer.
The son of an Italian mother and a Texan father, Jacobs was born in El Paso, Texas, on September 26, 1994.
He moved to Italy when he was one month old, settling in Desenzano del Garda, where he began practising athletics at the age of 10.
Jacobs lives in Rome with his partner Nicole and their two children, Anthony and Megan; he also has a son, Jeremy, from a previous relationship.
Jacobs’s victory came only moments after his countryman Gianmarco Tamberi tied Qatar’s Mutaz Essa Barshim for gold after both cleared 2.37m in the men’s high jump.
Lamont Marcell Jacobs and Gianmarco Tamberi embrace after both winning gold at the Tokyo 2020 Olympics, in Tokyo, Japan, on August 1, 2021. (Photo: AAP)
Tamberi, 29, and Barshim, 30, agreed to settle for joint gold after three failed attempts to clear the top height of 2.39 metres.
An Olympic official had offered a jump-off to decide the champion, at which point Barshim asked if they could share gold instead.
