The pair will join Luke Donald and Robert Karlsson as vice captains for the match at Whistling Straits in Wisconsin from 24-26 September.
Kaymer and McDowell will bring a broad range of knowledge and experience to the three-time Major winner’s backroom staff, having both starred in pivotal Ryder Cup moments as players.
Two-time major winner Kaymer will take on the vice captaincy role for the first time after four appearances as a player, during which time he won an individual total of 6.5 points.
The German has been on the winning side three times, famously holing the putt that sealed one of the most famous comebacks in sport in the “Miracle of Medinah” in 2012.
Kaymer will now be returning to the scene of his major breakthrough, having tamed Whistling Straits to secure the 2010 US PGA Championship.
McDowell ill be serving as a vice captain for a second time, having joined Harrington as part of the backroom team that helped Thomas Bjørn plot a stunning 17.5-10.5 victory at Le Golf National in France in 2018.
The former US Open champion has also appeared in the biennial contest on four occasions, claiming the winning point at Celtic Manor in 2010.
“I chose Graeme, first of all, based on the 2018 Ryder Cup,” said Harrington, speaking in a video conference from Germany where he is playing in this week’s BMW International Open. “He was a vice captain like I was, and his opinion really counted, what he said was spot on when he said it.
“I think he carries a certain amount of authority both in the vice captain’s team room and the actual players’ team room. The players look up to him. He's a solid opinion.
“With Martin, he actually brings a nice balance to my vice captains. I think he's known for having a very cool head under pressure and it is a pressure situation, the Ryder Cup. So, emotionally, he brings a nice level-headedness to what we're doing.
"I also think Martin is going to bring the perfect balance to my vice captains in the sense he will be a very cool hand in what can be quite a turbulent emotional scene when it comes to picking teams and everything that's going on in the locker room of a Ryder Cup.”
Both players are delighted to be taking on the roles in a match that will see Steve Stricker captain the Americans in his home state.
“When Pádraig approached me at the PGA Championship, I was a little surprised at that stage,” admitted Kaymer, also speaking from Munich. “It's such a huge honour that I really didn't know how to take it.
“We spoke a little bit about it at the Champion’s Dinner (at Kiawah Island) and I must admit I struggled a little bit to sleep because once I decide to do something, I would like to do it properly and in the right way. I wasn't really sure if I would be up for that task because I don't really know what it is about.
“Obviously I've played a few Ryder Cups and I only focused on my own game to contribute as much as possible to the team. The vice captain is a very special role and I’m really looking forward to the challenge.
“It will be a very positive challenge that I've never experienced before. And hopefully it will tell me something, also, about myself if I would be up for the task one day to be the captain myself.”
McDowell described it as a “great honour” adding: “We have a huge amount of talent in the room, and I learned a huge amount in 2018 about what it takes to be behind the scenes.
“I learned a huge amount about how to communicate with the players, what everybody needs, what the captain needs to help them do his job. I'm really, really excited to kind of get going and hopefully win the Ryder Cup at Whistling Straits.”
Harrington is set to leave it until his team has been finalised before adding a fifth vice captain, with Poulter a likely contender if he misses out on a playing role on this occasion and former Open champion Henrik Stenson as well.
The much-publicised spat between Bryson DeChambeau and Brooks Koepka is the last thing Stricker needs in the US team room, but Harrington said he is not paying too much attention to that.
“It's like people watching, isn't it, when you hear the stories and things going on, you're going, ‘it's of interest’,” said the three-time major winner. “But it doesn't really make a difference to how the players play the week of the Ryder Cup and I certainly wouldn't be relying on that.
“I'd be relying more on getting the most out of my team. I think that's what we do in The Ryder Cup now. You're not there to rely on the opposition playing badly. You're trying to make sure that your team plays as well as it can, believing that if all they have to do is play their own game, play as well as they can, and that's good enough.
“The best way you can go is let's hope they play well and we play better, and that will be what I'll be trying to instill into my team. We are not going to focus on them. Because you just don't know. You don't know how much of it is real.”