The 30-year-old, at her fifth Olympics, hit the wall first in the 50m free in 23.71sec ahead of Australia's Meg Harris (23.97) and China's Zhang Yufei (24.20).
It was only Sjoestroem's third career Olympic gold medal, compared to the 14 she has won at world championships.
"Well, this was definitely my best one with the two golds. I never thought I would win the two goals on my fifth Olympics," she said.
"It's unbelievable. I can definitely say, I'm not going to be better than this. Like this is the peak of my career for sure.
"So I mean, I'm so proud of what I've done the whole of my whole career."
Sjoestroem first made her mark at the 2009 world championships in Rome when she won the 100m butterfly gold and despite turning 31 later this month plans to continue swimming.
"I'm definitely going to continue swimming for many years, but I mean, how can I top this ever?"
She was always the favourite, winning the last three world titles after finishing second in Tokyo to Australia's Emma McKeon who did not qualify for the event in Paris.
Sjoestroem, the world record holder, has swum the six fastest times in history, including the third quickest ever in the semi-finals to fire a warning shot.
She also holds the world record over 100m, a title she won in Paris ahead of American Torri Huske and Hong Kong's Siobhan Haughey.
But she was not entirely happy with her race.
"I had a really, really bad breakout, like my first stroke was terrible," she said.
"But I knew before the race also that even if I do a few mistakes, I have a really high level.
"I was going in with confidence. Like I can continue doing under 24 seconds, any day, any time of the day. So I was like, trying to focus on that."
Winning silver was a dream come true for Harris who dipped below 24 seconds for the first time.
"I can't be more happy than that," she said.
"It took me a while to find out and line up all the times. I think it was shock. I was just sitting there like I have no idea what's going on."
