Laura Marsh hit 54, a career-best T20 score, as England made 133-6 after being put into bat.
Fellow opener and captain Charlotte Edwards posted 45 in a 102-run partnership with Marsh.
With nine wickets in hand, England attacked in the final five overs then their spinners dominated to bowl out Pakistan for 90 in the final over with Holly Colvin taking career-best figures of 4-9. Danielle Hazell took 2-19 while Marsh contributed a wicket maiden in her first over.
“We were pleased to get off to a good start today," Marsh said. "We played positive cricket and that’s how we play our game.
"It’s always good to contribute, we look to go out there and hit boundaries and Charlotte and I did that. We’ve worked hard as a team on knocking the ball into the outfield even when there isn’t so much pace on it, so we are not concerned about facing spin.
"All the bowlers bowled well today and there was another good team performance in the field. We’re all happy with our positive start to the competition and look forward to playing India on Saturday."
England top Group A along with Australia, who beat India by eight wickets in their opening fixture on Thursday. India set Australia a target of 104 and they cruised home with the loss of only two wickets.
Jess Cameron scored 36 off 35 balls after Erin Osbourne had done damage with the ball, taking 3-13.
Group B features West Indies, South Africa, Sri Lanka and New Zealand.
The women's tournament is taking place concurrently with the men's World T20 in Sri Lanka.
Women's World T20 fixtures:
Group B: New Zealand v South Africa (Galle) - Sep 28
Group B: Sri Lanka v West Indies (Galle) - Sep 28
Group A: Australia v Pakistan (Galle) - Sep 29
Group A: England v India (Galle) - Sep 29
Group B: South Africa v West Indies (Galle) - Sep 30
Group B: Sri Lanka v New Zealand (Galle) - Sep 30
Group A: India v Pakistan (Galle) - Oct 1
Group A: Australia v England (Galle) - Oct 1
1st Semi-Final: Colombo - Oct 4
2nd Semi-Final: Colombo - Oct 5
Final: Colombo - Oct 7
South Africa beat Sri Lanka by 6 wickets
West Indies beat New Zealand by 7 wickets
England beat Pakistan by 43 runs