England batsman Ollie Pope has moved to Welsh Fire for The Hundred in 2021 and opener Rory Burns has switched to Oval Invincibles.
Pope left Southern Brave and Burns moved from London Spirit as part of a reallocation of England's Test players.
Eight women's players, including West Indies' Deandra Dottin and Stafanie Taylor, have been confirmed for 2021.
The launch of the 100-ball competition this summer was postponed by a year because of the coronavirus pandemic.
All women's players have been given the option of keeping their 2020 deals.
Eighteen players have been confirmed for 2021 - eight women's players to have already taken up the option and 10 men's players with Test central contracts for next season.
Why are Pope and Burns moving teams?
Last year, the eight men's teams chose a player with an England Test contract for 2019-20 but, after the 2020-21 central contracts were announced last month, teams containing two centrally contracted players in their 15-player squads had to decide which one to keep.
Southern Brave had Pope and pace bowler Jofra Archer in their squad.
Welsh Fire, however, were without a centrally contracted Test player after wicketkeeper Jonny Bairstow lost his deal. They were therefore able to sign 22-year-old Pope, who has been awarded a Test contract for the first time.
Batsman Zak Crawley, who also received his first central contract, was already part of the Spirit squad, while Burns was released and moved to the Invincibles - one of two teams who can sign two England Test players.
Dom Sibley, unsigned in the 2020 draft but now a centrally contracted player, has joined Birmingham Phoenix.
First batch of players confirmed for The Hundred in 2021
Men's Women's
London Spirit Zak Crawley Deandra Dottin
Oval Invincibles Sam Curran, Rory Burns Fran Wilson
Birmingham Phoenix Chris Woakes, Dom Sibley Amy Jones
Southern Brave Jofra Archer Stafanie Taylor
Northern Superchargers Ben Stokes Lauren Winfield-Hill
Trent Rockets Joe Root Nat Sciver
Welsh Fire Ollie Pope Katie George
Manchester Originals Jos Buttler Kate Cross
James Anderson and Stuart Broad are the only England men's players with Test central contracts to opt out of The Hundred
New deal 'a weight off my shoulders'
England women's bowler Katie George, who is among those to roll over her contract for 2021, said she never considered moving from Welsh Fire.
"Nothing had changed with my conversations with [head coach] Matthew Mott and having [Australia captain] Meg Lanning as captain, which I hope will be the same next year," 21-year-old George told BBC Sport.
"I was very excited to play this year and am probably even more excited now with the anticipation."
She said the move by the England and Wales Cricket Board (ECB) to allow players to roll over their contracts and salaries was a "weight off your shoulders".
"It shows the ECB is backing us and backing the women's game," she said. "They want to invest in it and want to commit long term to that."
Will more players move?
A 'retention window' has opened for men's teams to renegotiate with their players over new deals for 2021.
Teams can keep any player they signed for the 2020 tournament and move them up or down salary brackets, which have been reduced by 20% because of the pandemic.
Bairstow, for example, can be retained by Welsh Fire but would have to take the place of another player in one of the seven salary bands after losing his England deal.
The retention window will close at the end of January 2021 and any players not retained will go into a new draft to fill the remaining spaces. The draft can also include players unsigned for 2020.