At the 2008 Summer Olympics in Beijing, China, Grevers won two gold medals by swimming in the preliminary heats of the 4×100-meter freestyle relay and 4×100-meter medley relay (swimming the backstroke leg) as the Americans went on to win the finals in those events and medals are awarded to participants at any step along the way. Grevers also won an individual silver medal in the 100-meter backstroke in a time of 53.11-second, 0.57 of a second behind the winner, world record holder Aaron Peirsol.
At the 2009 World Aquatics Championships, Grevers was part of U.S. men's 4×100-meter freestyle relay team who took the gold ahead of Russia and France. Grevers also earned a gold in the 4×100-meter medley relay for his contributions in the heats.
At the 2012 United States Olympic Trials, the qualifying meet for the 2012 Olympics, Grevers qualified for the U.S. Olympic team by finishing first in the 100-meter backstroke and third in the 100-meter freestyle. In the final of the 100-meter backstroke, Grevers won in a time of 52.08 seconds, the second-best effort of all time and just behind Aaron Peirsol's world record of 51.94. Grevers recorded the fastest time in a textile suit in the 100-meter backstroke. In the 100-meter freestyle, Grevers placed third with a time of 48.55, which ensured him a spot on the 4×100-meter freestyle relay. Grevers also competed in the 50-meter freestyle, and placed sixth in the final with a time of 22.09.
At the 2012 Summer Olympics in London, Grevers won a total of three medals: two golds and one silver. Grevers earned his first medal, a silver, by swimming for the second-place U.S. team in the preliminary heats of the 4×100-meter freestyle relay. In the final, the American team finished second behind France. Teaming with Jimmy Feigen, Ricky Berens, and Jason Lezak in the heats, Grevers swam the second leg and recorded a time of 47.59. After leading the heats (52.92) and semi-finals (52.66) of the 100-meter backstroke, Grevers won gold in the final of the 100-meter backstroke with a time of 52.16, bettering Aaron Peirsol's Olympic record of 52.54 set in 2008 and 0.76 s ahead of Nick Thoman. For Grevers, it was his first individual gold medal. In his final event, the 4×100-meter medley relay, Grevers won gold with Brendan Hansen, Michael Phelps and Nathan Adrian. Swimming the backstroke leg, Grevers recorded a time of 52.58 seconds, and the U.S. team went on to win with a time of 3:29.35.
At the 2013 FINA World Championships in Barcelona, Grevers achieved a total of two medals: a gold and a silver. On the first night of swimming, Grevers missed the top-eight championship roster in the 50-meter butterfly, as he finished his semi-final run with a twelfth-place time in 23.35. The following day, Grevers threw down the event's fastest time of 52.93 to claim the gold medal in the 100 m backstroke, finishing ahead of his teammate David Plummer by nearly two-tenths of a second. On the final night of the meet, Grevers swam his last two finals with only 45 minutes in between. First, he posted a matching time of 24.54 to share the silver medal with France's Jérémy Stravius in the 50 m backstroke. Nearly an hour later, Grevers teamed up with Kevin Cordes, Ryan Lochte, and Nathan Adrian for the final in the 4 × 100 m medley relay. During the race, Grevers swam the backstroke leg and touched the wall with a split of 53.02 until his teammate Cordes left the block 0.04 seconds early on the breaststroke leg, smashing the medal chances entirely for the Americans with a disastrous disqualification.
He did not make the 2016 Olympics Team as he finished third in the 100m backstroke.
Grevers was born in Lake Forest, Illinois. He graduated from Lake Forest High School, and then attended Northwestern University in Evanston, Illinois, and swam for the Northwestern Wildcats swimming and diving team.
Both of Grevers's parents are from the Netherlands. Grevers considered representing the Netherlands and even spoke about it with Dutch swimming legend Pieter van den Hoogenband. Ultimately, he decided to represent the United States.
Grevers proposed to his wife, Annie Chandler, at the Missouri Grand Prix on Saturday February 11, 2012. The couple were married on April 6, 2013 in San Antonio, Texas.
Annie gave birth to the couple's first child, a daughter, named Skylar Lea Grevers on November 9, 2016.