Exeter Chiefs and Sale Sharks have been granted places in the top flight of women's rugby in England for three years, starting from next season.
Richmond and Firwood Waterloo Ladies have lost their places in the Premier 15s as a result after their re-applications were rejected.
Both had the right of appeal, but have confirmed they will not do so.
Richmond were the powerhouse of women's rugby at the turn of the century, winning the old Premiership five times.
The 2019-20 season was cancelled on 20 March because of the coronavirus pandemic, along with all men's leagues below the Premiership.
Nicky Ponsford, the RFU's Head of Women's Performance, said both Exeter and Sale - who have the support of their respective Premiership men's clubs - would "undoubtedly add quality to the decision both on and off the field".
Sale have appointed Darren Lamon as their first head of women's rugby.
Exeter are still waiting to see when, and if, the men's Premiership - which they lead - will resume, but chief executive Tony Rowe was delighted by the elevation of their women's side.
He said: "This is the news we have been waiting for. After months and months of hard work behind the scenes, this is the real reward.
"I wanted to start a women's side many years ago. We looked at the idea when the first applications for the Tyrrells Premier 15s division were out, but we weren't in a position to go forward at that time.
"Today represents another huge milestone in the history of our great club and it further enhances our aim of creating the rugby giant that is Exeter Chiefs Rugby Club.
Sale co-owner Michelle Orange said: "The opportunity to establish Sale Sharks Women will complete our family unit and help us play our part in reinforcing the importance of sport for all, be it as a participant or spectator or supporter.
"We look forward to building our women's team and seeing the resumption of play across all facets of rugby union."
Bristol Bears, Gloucester-Hartpury, Harlequins, Loughborough Lightning, Saracens and Wasps were already guaranteed places in the 10-team Premier 15s until the end of the 2022-23 season as the top-six ranked sides.
All other clubs had to re-tender alongside any potential new entrants and following initial submissions, the RFU completed the interviews via conference calls two weeks ago and as a result of that process, Worcester Warriors and DMP Durham Sharks also retained their places.
Since the introduction of the Premier 15s, Richmond have struggled to keep the pace with other sides, particularly those supported by men's professional clubs.
Before this season finished due to the coronavirus outbreak they were ninth in the table, with Firwood Waterloo Ladies bottom, both with only one win.
Following the RFU decision, Richmond described it as "another blow for traditional rugby clubs".
They said in a statement: "Richmond Rugby has been at the forefront of women's rugby for nearly 35 years and to this day remain one of the most successful women's clubs in world rugby.
"As such, today's announcement is very disappointing and upsetting for our current and former players, coaches, staff, sponsors, members, volunteers and supporters. "
Firwood Waterloo said: "We have always blazed the trail for Women's Rugby Union in the North West and are proud to have been a founder member of the league.
"Unfortunately in sport, for some teams to win, others have to lose and we were unable to find enough wins on and off the pitch over the first three years to retain our place."
Since the inception of the league in 2017-18, Saracens won the first two titles and were on course to add a third crown before the season was halted by coronavirus.
Sarries were two points clear at the top of the table when the RFU declared the Premier 15s season "null and void" as there was no promotion or relegation to take into account.
Meanwhile, the RFU has also confirmed that the Premier 15s Development League will no longer take place from next season.