The 27-year-old clocked 21.55 seconds to complete the sprint double in Kingston having won the 100m on Friday.
Olympic champion Elaine Thompson-Herah was second in 22.05, with Shelly-Ann Fraser-Pryce third in 22.14.
Jackson’s time puts her behind only world record holder Florence Griffith Joyner (21.34) and Thompson-Herah (21.53) on the all-time list.
“Honestly, I am shocked by the time,” said the Olympic bronze medallist. “I never expected to go that fast.
“I knew that I had something special in my legs but to run that fast… I’m just grateful.”
Elsewhere, Andrew Hudson – who recently switched allegiance from the United States – won the men’s 200m in 20.10, beating 100m champion Yohan Blake and Nigel Ellis.
Olympic champion Hansle Parchment won the men’s 110m hurdles, having recovered from a slow start to catch 2016 Olympic and 2017 world champion Omar McLeod – who then hit a hurdle and finished in last place.