The 26-year-old American, who was sexually abused as a teenager by a former coach, beat Audrey Tcheumeo of France in the women's under-78kg final.
Harrison started the the final in aggressive fashion against a strangely subdued Tcheumeo.
The French woman was leading their head-to-head 5-4 but was twice penalised for passivity as she struggled to get a grip on the contest between two former world champions.
With the clock ticking down and Harrison on the brink of being crowned champion, she made sure by wrenching out Tcheumeo's arm and forcing a submission.
The powerful Harrison had also armlocked Slovenia's Anamari Velensek in the semi-final.
Brazil's Mayra Aguiar jumped into the stands to hug and kiss friends and family after winning bronze in a close fought bout against Yalennis Castillo of Cuba.
Determined to milk her moment on home soil, Aguiar, another former world champion, needed some coaxing from her coach to come down from the tribunes.
Velensek took the other bronze after a long battle to choke out Germany's Luise Malzahn, who finally submitted as her nose started to bleed.