Dean, the 21-year-old off-spinner, takes over from the vastly experienced Knight, who missed England's entire Commonwealth Games campaign - they lost the bronze-medal play-off to New Zealand - with a hip injury that has left her needing to use crutches and is expected to keep her on the sidelines for a period of months.
"It's a great opportunity for me, I'm really looking forward to leading this team," Dean said. "Obviously, we are gutted that Heather can't join us this year, but we have an exciting squad filled with experience and young talent and we can't wait to get started on Friday."
A relative newcomer to the England set-up, Dean earned her only T20I cap for England during the washed-out second match in that leg of the Ashes series in January. She didn't take the field as play was abandoned in the fifth over with England 25 without loss. Dean was not part of England's squad for the Commonwealth Games, which was played as a T20 competition.
She has played 16 ODIs, making her debut against New Zealand last September, most recently in the series with South Africa, which she finished as leading wicket-taker.
Dean was key to Southern Vipers' Charlotte Edwards Cup triumph in June, taking two wickets and sharing a match-winning partnership with Ella McCaughan to help defeat Central Sparks by six wickets in the final. She was also the competition's second-highest wicket-taker.
In 2021, she took six wickets for London Spirit, who finished their inaugural campaign in fourth place on the eight-team table, at an average of 28.00 and an economy rate of 7.09. During that time, she impressed Knight and made her international debut a short time later.
Dean will lead an impressive international contingent at London Spirit, including two Australian Commonwealth Games gold medallists in Beth Mooney - the Games' leading run-scorer - and fast bowler Megan Schutt, as well as talented New Zealand allrounder Amelia Kerr.
London Spirit open their 2022 season against Southern Brave, last year's runners up, in Southampton on Friday.