Plenty of movement at Wasps
Wasps also confirmed the signings of wing Marcus Watson and prop Ben Harris, who will arrive at the club from Newcastle Falcons ahead of the 2017-18 campaign.
Harlequins Director of Rugby John Kingston was delighted with his buy.
"He is a proven and experienced tighthead prop who will give us the necessary strength in depth in a key position," Kingston said of Swainston.
"In my conversations with him, he has displayed a real hunger to be a regular starter and I have no doubt he will provide strong competition for the other props in our squad."
An established Premiership player, the 27 year-old has made over 80 appearances for Wasps since joining in 2012. The former Leeds man, who began his career at Harrogate, was called into the 2012/13 England Saxons squad to play Scotland A.
"The opportunity to join Harlequins was one that I just couldn't turn down," Swainston said.
"To be able to work under the expert guidance of Graham Rowntree and Adam Jones is something that I'm really excited about.
"My attention will turn to Harlequins in the summer, but for now I will be doing all that I can to finish the season with Wasps on a high. I am really grateful for the help and support that Dai Young and Wasps have given me during my time."
* Meanwhile Wasps revealed that in addition to the Sevens flyer (Watson) and loosehead prop (Harris), the club will also be joined by Solihull-born hooker Antonio 'TJ' Harris, who is currently playing his rugby in the Championship with Nottingham Rugby.
Known for his explosive power, Harris will add to Wasps' talented pool of hookers next season, which includes Tommy Taylor, Ashley Johnson and Tom Cruse.
The 25-year-old Watson helped Great Britain Sevens win a silver medal at the Rio Olympics and has also represented England in the World Rugby Under-20 Championship.
Ben Harris will return to Wasps next season, having impressed during his short-term loan stint with the club. The England Counties prop previously represented Yorkshire Carnegie and Rotherham Titans before joining Falcons.
Speaking about the recruits for the new campaign, Wasps' Director of Rugby, Dai Young said: "We're pleased to bolster our front row options for next season, with the addition of Ben Harris and TJ Harris. We already know a lot about Ben and believe he has real potential at this level. TJ Harris has also impressed us in the Championship and we think he still has lots of growth in him. At only 22, he will only get better and we're sure they will both become valuable members of our squad.
"Marcus Watson will be another exciting addition to our backline. Everyone has seen how Wasps like to play rugby. We always want an exciting back three, with pace on the wing, as we feel we have great distributors in our inside backs so we want to make sure we have deadly finishers to execute the chances they create. Marcus certainly fits into that category brilliantly, as he has shown already at international level on the 7s circuit and in the Premiership.
"Every squad is ambitious to evolve and improve, so it's important to keep one eye on the future and make sure all the building blocks are in place to continue the squad's progression.
"I'm already very happy with the squad we have developed here at Wasps and we're now in a place where we only need to make a handful of new signings, rather than 12-13 as in previous years.
"Continuity is really important, so it's very much a case of adding to the talent we already have and making sure we have at least two quality players in each position, to provide the depth needed to be consistently competitive at the highest level.
"For the players, the focus is very much on what can be achieved this season and ensuring we improve our performances, so we're still fighting at the top of the Premiership come the business end of the season."
Speaking about the move for next season, Marcus Watson said: "Firstly, I'd like to say thanks to all the coaches, staff and fans at Newcastle for giving me an opportunity to return from 7's to the Premiership. I have really enjoyed my time with the club and look forward to helping them finish the season on a high.
"Wasps are a club playing hugely exciting and expansive rugby at the top of the Premiership and I'm delighted to have the opportunity to be part of that next season. Every player wants to be able compete for trophies in their career and I believe I can do this both domestically and in Europe with Wasps, which is really exciting!"
Ben Harris added: "I've thoroughly enjoyed my time at Newcastle Falcons and would like to thank the club and coaches for giving me the opportunity to play in the Premiership. There's a great set of lads and supporters at the Falcons and I really appreciate the support Micky Ward and Scott Macleod have given me with my game. For the rest of the season, I will be doing everything I can to help the Falcons continue the good run we're on.
"I'm really looking forward to being part of the environment and set-up that Wasps are creating in Coventry. Being able to develop my game under the tutelage of Dai Young, as both a Director of Rugby and a world class prop, is a huge draw. I'm excited to see how I can improve as a player and what part I can play as the squad continues to build on the performances they've already produced this season."
TJ Harris said: "First of all, I'd like to thank Nottingham Rugby Club and all the members of staff involved who have helped & supported me for my two seasons at the club. When I was offered the opportunity to join Wasps, I couldn't resist as I'd have the chance to join a fantastic club, competing at the top of the Premiership, and move back home to Coventry.
"I understand how much hard work and responsibility will be needed once I move, but I will take that as a challenge. It will be brilliant to be around so many talented players and hopefully I will be able to learn from them and develop my game as much as possible, to be able to help the team succeed."