[10][11] At the 2011 World Aquatics Championships in Shanghai, China, Dwyer swam in the heats of the 4×200-meter freestyle relay and earned a gold medal when the United States won in the final.

Teaming with David Walters, Ricky Berens, and Peter Vanderkaay, Dwyers swam the second leg and recorded a time of 1:47.31.

At the 2013 World Aquatics Championships in Barcelona, Spain, Dwyer earned his first medal, a silver, by swimming for the U.S. team in the preliminary heats of the 4×100-meter freestyle relay.

In his first individual event, the 200-meter freestyle, Dwyer won silver behind Frenchman Yannick Agnel, recording a personal best time of 1:45.32.

In the 4×200-meter freestyle relay, Dwyer combined with Ryan Lochte, Charlie Houchin, and Ricky Berens, with the team finishing in first place.

Dwyer was again part of the US 4 × 200 m freestyle team that won gold, leading off the relay in the final to teammates Townley Haas, Ryan Lochte and Michael Phelps.

Dwyer also won a bronze medal in the 200 m freestyle individual event after a late surge, behind Sun Yang and Chad le Clos.

In October 2019, Dwyer was handed a 20-month competitive ban after testing positive for an anabolic agent by the U.S. Anti-Doping Agency (USADA).

[18] The American Arbitration Association found that Dwyer consulted on health issues with his trainer Reardon and obstetrician-gynecologist Dana Russo, and the latter concluded his testosterone levels were in the 5th percentile.

Thereafter, Dwyer was using a hormone therapy product BioTe, plant-derived testosterone, that were implanted as pellets beneath the skin in October 2018.

[19] Russo told the arbitration panel that she had asked someone on the United States Olympic & Paralympic Committee if the treatment was allowed, but the person could not be identified.

[21] In 2019, Dwyer was the face of Philippine-based international clothing brand BENCH's men's wear campaign in the United States and North America.