The medal makes Oleksiak the most decorated Canadian athlete to ever compete at the Summer Games.
Her six-medal haul also ties the 21-year-old with the most decorated Canadian athletes in any Olympics, joining speed skater Cindy Klassen and cyclist and speed skater Clara Hughes in the record books.
Oleksiak finished with a time of 1:54.70, just over a second behind gold medal winner Ariarne Titmus of Australia, who set a new Olympic record. Hong Kong's Siobhan Bernadette Haughey nabbed the silver.
The race also proved to be disappointing for American favourite Kathleen Ledecky, who took the gold medal in the same event at the 2016 Summer Games in Rio and has also won six Olympic medals overall -- all but one of which are gold.
Oleksiak's win comes after she took the silver medal in the women's 100-metre freestyle relay, which she won with three other teammates on Sunday.
It's also the latest medal won by Canada's women swimming team, which has earned a gold in the 100-metre butterfly and a silver in the 100-metre backstroke.
In addition to her two Tokyo medals, Oleksiak won four medals at the 2016 Games, the first Canadian ever to do so in a single Summer Olympics. She was also Canada's youngest-ever Olympic champion at just 16 years old.
Oleksiak will continue to seek her third medal of the Games later on Wednesday when she swims in the 100-metre freestyle semifinal.