2012: First Olympics

At the 2012 U.S. National Championships, Mikulak won the bronze medal in the individual all-around and silver medal on the individual parallel bars event.^[7] At the 2012 U.S. Olympic Trials, he was unable to compete in five of the six events on Day 2 after spraining his ankle while competing on vault on the first night of competition.^[5][8][9] Despite the injury, Mikulak was selected for the five-man Olympic gymnastics team.^[10] He was the first male gymnast from the University of Michigan to be named to the U.S. Olympic team.^[11]

At the 2012 Olympics in London, Mikulak placed 5th with the U.S. team in the team competition. The U.S. team had placed 1st in the qualification round. Mikulak competed in the vault final, placing 5th. His Michigan teammate Syque Caesar also competed in the 2012 Summer Olympics, representing Bangladesh.^[5]

2013: First national title

Mikulak won his first national all-around title at the 2013 U.S. National Championships in Hartford, Connecticut. He also won the gold medal on parallel bars and high bar. He then competed at the 2013 World Championships, where he placed 6th in the individual all-around final and 4th in the individual high bar final.^[12]

2014: Second national title

In March at the 2014 American Cup in Greensboro, North Carolina, Mikulak won the all-around title. In August, Mikulak won his second national all-around title at the 2014 U.S. National Championships in Pittsburgh, Pennsylvania. He also won the gold medal on pommel horse and the silver medal on high bar. He then competed at the 2014 World Championships in Nanning, China. He won a bronze medal with the U.S. team in the team competition and placed 12th in the all-around final.

2015: Third national title

In March, Mikulak, along with Simone Biles, MyKayla Skinner and Donnell Whittenburg, represented the U.S. against a strong international field at the 2015 AT&T American Cup at AT&T Stadium in Arlington, Texas. Mikulak finished fourth in the individual all-around event.

On July 11, 2015, Mikulak led the U.S. men's gymnastics team to their first gold medal at the Pan-American Games in twenty years. Two days later, he was crowned Pan American champion in the all-around final.^[13]

On August 16, 2015, Mikulak won his third consecutive national all-around title at the 2015 U.S. National Championships in Indianapolis. He also won the gold medal on vault and parallel bars and won the bronze medal on pommel horse and high bar.^[14] Due to a partially torn achilles tendon injury, he was unable to participate at the 2015 World Championships in Glasgow, Scotland.^[15][16]

On December 17, 2015, Mikulak and two-time World medalist Donnell Whittenburg accepted invitations to represent the U.S. at the 2016 American Cup in Newark, New Jersey, on March 5, 2016.

2016: Fourth national title and second Olympics

On February 21, 2016, Mikulak won the all-around title at the 2016 Winter Cup in Las Vegas, with a two-day score of 177.50. He outscored the second-place finisher, Akash Modi, by over two points. In March, Mikulak finished fourth at the American Cup, his first international competition since recovering from a torn achilles tendon. In April, he competed at the 2016 Pacific Rim Championships and won the gold medal with the U.S. team in the team event. He also won the bronze medal in the all-around and the silver medal on the pommel horse.

Mikulak claimed his fourth consecutive national all-around title on June 5, 2016, at the 2016 U.S. National Championships in Hartford, Connecticut. He outscored Chris Brooks 181.500 to 179.850 to become the first male gymnast to win four consecutive national titles since Blaine Wilson won five titles in a row from 1996 to 2000.

On June 25, 2016, Mikulak placed first at the 2016 U.S. Olympic Trials in St. Louis, Missouri, and qualified for his second Olympic team. He was named to the five-man U.S. Olympic men's gymnastics team along with Chris Brooks, John Orozco (who was replaced by Danell Leyva due to injury), Jake Dalton, and Alex Naddour.^[17] Mikulak was one of three gymnasts who train at the U.S. Olympic Training Center in Colorado Springs, Colorado, to qualify for the Olympic men's gymnastics team.

At the 2016 Olympics in Rio de Janeiro, Brazil, Mikulak placed fifth with the U.S. team in the team competition. He went on to place seventh in the all-around final and fourth in the high bar final. The U.S. men's team had placed second in the qualification round.

2017

In August, Mikulak only competed on two events at the 2017 U.S. National Championships in Anaheim, California and maintained his spot on the U.S. national team. His streak of four U.S. national all-around titles was snapped, as he was still recovering from an achilles tendon injury that he suffered in February at the Winter Cup. He won the silver medal on pommel horse and the bronze medal on high bar. In October, he competed only on high bar at the 2017 World Championships in Montreal, Canada, as he was still not fully back from his injury. His quest to capture an individual medal ended when he fell on high bar during the qualification round. As Mikulak was recovering from injury, he continued to host and participate in numerous clinics and workshops for aspiring gymnasts.

2018: Fifth national title and first world individual event medal

In February, Mikulak won the gold medal in the all-around at the 2018 Winter Cup in Las Vegas. He also placed first on the floor exercise, parallel bars and high bar. Following the Winter Cup, the top six ranked all-around gymnasts including Mikulak automatically qualified for the 2018 U.S. national team. In April, he competed at the 2018 Pacific Rim Championships and won the gold medal with the U.S. team and the all-around title. He also won the gold medal on rings and high bar and won the silver medal on floor exercise and parallel bars.

In August, Mikulak won his fifth national all-around title in dominant fashion at the 2018 U.S. National Championships in Boston. After a somewhat shaky performance on Day 1 that included falls on pommel horse and high bar, he came back with a very strong outing on Day 2 and won the gold medal easily. His margin of victory was the largest of any of his national titles at the time (he would extend this record in 2019). He also won the gold medal on floor exercise, parallel bars and high bar. Mikulak is the first male gymnast to win five U.S. national titles since Blaine Wilson won five straight crowns from 1996 to 2000.^[18]

In October, Mikulak competed at the 2018 World Championships in Doha, Qatar. He and the U.S. team finished fourth in the team competition. He qualified for the individual all-around final in third place, and also for four event finals. Mikulak is the first U.S. man since Kurt Thomas in 1979 to qualify for that many event finals at one World Championships.^[19] In the individual all-around final, he had strong competition and was in third place heading into the last event, high bar, where a costly error left him in fifth place. This result was the best finish at Worlds by a U.S. man since 2011.^[20] In the individual event finals, Mikulak broke through and won his first World individual event medal, a bronze on high bar. Before the high bar final, he had placed seventh on floor exercise, and fourth on pommel horse and parallel bars.

2019: Sixth national title

In February, Mikulak placed first on floor and horizontal bars, and second on parallel bars and all-around at the 2019 Winter Cup.

In March, Mikulak placed second in the all-around at the 2019 American Cup, an FIG All-Around World Cup event, just 0.001 of a point behind fellow American and the event's two-time defending champion Yul Moldauer.

In April, Mikulak competed at the 2019 FIG All-Around World Cup in Tokyo, Japan, an individual all-around only event in which he was the defending bronze medalist. He went on to win the all-around gold medal with a score of 86.599 ahead of the defending gold and silver medalists from Japan— Kenzō Shirai (82.964), who won the bronze medal while still recovering from injury, and Wataru Tanigawa (85.665), who successfully defended his silver medal.

In August, Mikulak competed at the 2019 U.S. National Championships. He won his record-breaking sixth all-around title, as well as gold medals on floor exercise, pommel horse, parallel bars, and high bar. His margin of victory in the all-around was the largest of any of his national titles.

In summer 2020, Mikulak announced he was in his final full year of competition, culminating, he hopes, with representing the United States at the 2021 Summer Olympic Games in Tokyo.

2020

At the 2020 Winter Cup in Las Vegas, Nevada, Mikulak finished first in all-around and parallel bars, second on floor and high bar and third on pommel horse.

2021: Third Olympics

At the 2021 U.S. Gymnastics Championships in Fort Worth, Texas Mikulak finished first on high bar, third all-around, sixth on parallel bars and eighth on floor and still rings. At the Olympic Trials he finished fourth in the all-around, first on floor exercise, and second on high bar. As a result, Mikulak was chosen by the selection committee to represent the United States at the 2020 Summer Olympics alongside Brody Malone, Yul Moldauer, and Shane Wiskus.^[21][2]

In 2021, Mikulak started speaking out about his experiences with mental illness as an athlete. In May, he spoke at a USA Gymnastics athlete-driven panel about mental health.^[22][23] Mikulak described feeling overwhelmed by his focus on gymnastics during the 2016 Olympics cycle, including during the Olympic Floor Exercise finals. He had posted the highest qualifying score in the field, but he did not win a medal in the event finals, even though several other contenders had made errors.^[23] Mikulak also described his struggles with depression after the postponement of the 2020 Summer Olympics.^[24] Mikulak called the 2020 games the most "meaningful" and the "hardest" Olympics to qualify for in his career.^[25] He spoke about redefining his identity beyond only being a gymnast.^[23]

In 2021, Mikulak was honored with the National Polish-American Sports Hall of Fame Excellence in Sports Award for the year 2020, in Troy, Michigan.