The 33-year-old US superstar, who won her 19th Grand Slam title in Australia this year, lifted the trophy in the elite premier level tournament for the third straight year.
She also won three straight Miami titles from 2002-04 and back-to-back titles in 2007-08.
Williams had already surpassed Steffi Graf for most Miami triumphs with her win last year.
On Saturday she joined Graf, Martina Navratilova and Chris Evert as the only Open Era players to win the same event at least eight times.
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"It feels really good to have eight under my belt," Williams said.
"Can't say I thought I would win eight, especially in the beginning of the week," added the champion, who had struggled with her serve and unforced errors in previous matches.
"I had a couple matches where I had nearly 60 unforced errors in both, so I just needed to kind of get my mind back there and say, 'Serena, you normally don't play like this, so just go to how you normally play," she said of how she tried to regroup after clawing past world number three Simona Halep in the semi-finals.
- Serena's the best -
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World number 12 Suarez Navarro, playing in the biggest final of her career, wasn't surprised to find the winners zinging past her from every part of the court.
"When I play with Serena I know that she's the best," Suarez Navarro said. "She has the game to make me play bad.
"But this time I believed in me, in how I'm playing the other matches. I tried. I tried until the last point, but it was tough and difficult for me.