Swift, who rejoined the British squad this season after two years at UAE Team Emirates, will stay at the team until 2021, while Dunbar, who joined in late 2018, has agreed a three-year deal.
For the 31-year-old Swift, the season has marked a mental turnaround after recovering from an early season training crash which saw him suffer a ruptured spleen.
"I feel like I’ve found a renewed enthusiasm and motivation for the sport this year, so this new contract feels rewarding for many reasons," he said in a statement issued by the team.
"I think that’s down to the team and the way I’ve been riding this year. When you’re really happy somewhere and the environment of the team suits you like it does for me here, it really helps you to get the very best out of yourself."
Swift had spent eight seasons at what was then Team Sky before heading to UAE Team Emirates in 2017. Career highlights have included multiple stage victories across WorldTour races, the Tour of California, Tour de Pologne, Vuelta al País Vasco, Tour de Romandie and the Tour Down Under.
The Yorkshireman, who is set to lead Great Britain at this year's World Championships in the county, has also finished twice on the podium at Milan-San Remo. This year he won the British National Championships road race at the eighth time of asking.
"I don’t think anybody was expecting me to get back to the levels I’ve achieved this year," he said. "So it's hugely satisfying. It’s been a really pleasing season so far.
"The Worlds in Yorkshire aren’t far from where I grew up, so it’s massive opportunity for me to try and improve on my fifth place in Bergen two years ago. It’s going to be a tough ask, it’s going to be a very difficult race – but I’ll do everything I can."
Dunbar renews until 2022
Young Irishman Eddie Dunbar has had another three years added to his Team Ineos deal. The 23-year-old joined the team after Aqua Blue Sport shut up shop before the 2018 season ended.
After signing with the team in mid-September, Dunbar helped Gianni Moscon to victories at the Coppa Agostoni, Giro della Toscana and the Tour of Guangxi.
This season he has taken third place on stage 12 of the Giro to Pinerolo, and also finished on the podium at the Tour de Yorkshire and the Irish National Championships in the road and time trial.
"I was over the moon when I found out it was a three-year deal and I was going to be able to stay and learn from the best riders in the world," said Dunbar in a Team Ineos statement. "I am delighted to receive the opportunity to develop in this atmosphere."
"Having three years gives you time to work with the team, come up with a long-term plan to see what works for you, and the chance to grow with the team."
As well as his various podium spots, Dunbar raced his debut Grand Tour this season, finishing 22nd at the Giro d'Italia and improving as the three-week race progressed.
He's part of a growing youth movement at Team Ineos, racing alongside young talents such as Iván Sosa, Pavel Sivakov, Tao Geoghegan Hart and Tour de France winner Egan Bernal.
"We have a lot of young guys in the team that have all impressed this year, with Pavel doing really well at the Giro, Egan winning the Tour de France and Chris [Lawless] winning Tour de Yorkshire," he said. "There’s been a lot of standout performances from young riders and that’s a very positive thing going forwards.
"I’d like to go back and take on the Ardennes again as they’re definitely races I’d like to improve on. Of course, it would be good to ride another Grand Tour, whether it be the Giro, Tour de France or Vuelta, I don’t mind – but it would be great to get another opportunity in one of those races."
Team Ineos have already confirmed the contract renewals of Owain Doull and Chris Lawless through to the end of 2021, as well as the arrival of Giro d'Italia winner Richard Carapaz from Movistar. Diego Rosa is the only confirmed outgoing rider so far during this transfer window, joining Nairo Quintana at Arkéa-Samsic.