Melissa Thompson, 27, wrote a passage in just under 26 seconds, shaving off nearly 10 seconds from previous record holder.
She texted: "The razor-toothed piranhas of the genera Serrasalmus and Pygocentrus are the most ferocious freshwater fish in the world. In reality they seldom attack a human."
The Guinness World Record was earlier held by American Franklin Page who wrote the same passage in March this year.
Thompson, from Salford in Greater Manchester, used Samsung's new Galaxy S smartphone to break the record. Her record is subject to Guinness approval.
Thompson was shopping with her boyfriend, Chris Davies when they visited a Samsung roadshow where she had a go at the record.
"I used to send a lot of text messages - 40 or 50-a-day to Chris alone - so we both knew I could type fast. But since we moved in together and I started my job I haven't been texting as much and, you could say, my fingers were out of shape.
"It's a real shock to find out that I'm the fastest texter in the world," The Sun quoted her as saying.
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