The Polish seventh seed gained an early advantage in the first set when the world No 2 gave up a break point on back-to-back double faults.
That was all the room Swiatek needed as she continued her stellar form from earlier in the tournament to race away with the opening set.
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Unforced errors continued to cost Rybakina into the second set, as two missed backhands gifted Swiatek another break.
Rybakina was able to stave off one championship point, but Swiatek converted on her second opportunity to clinch her first title since last September.
Speaking at the post-match awards ceremony, Swiatek dedicated her victory to "everyone who is dealing with unfair judgement and hate".
She said: "Just keep pushing, keep growing, keep focusing on yourself because you know what's best for you.
"Always remember what's ahead and what might be possible."
In the men's draw, American Ben Shelton retained his crown by eclipsing compatriot Brandon Nakashima 6-3 7-6 (7-4) in Montreal.
Shelton did not drop a set throughout the tournament and is just the fourth man this century to go back-to-back at the event, joining Andy Murray, Novak Djokovic and Rafael Nadal.
He told atptour.com: "For me to play the way that I played this week to go through this draw speaks to the work I have been putting in.
"It also speaks to my mental toughness, my ability to focus through everything that was going on this week."
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