Arop competed for
Mississippi State in the 2018
NCAA Division I Outdoor Track and Field 800 m in Eugene, Oregon, finishing in second place. He won the gold medal in the
800 m at the
2019 Pan American Games, setting a new Pan American record in the process. He then made his
World Championship debut at the
2019 edition in
Doha. Qualifying to the final of the
800 m, he finished seventh. After the World Championships, Arop decided to end his amateur career and turn professional full-time, though the onset of the
COVID-19 pandemic meant that the 2020 athletic season was largely cancelled. In 2021, Arop competed in his first full professional season, making his first
Diamond League podium with a silver medal at the
BAUHAUS-galan in
Stockholm. In his next event that season, the
Prefontaine Classic on the
2021 Diamond League circuit, Arop claimed the gold medal ahead of the reigning Olympic gold and silver medallists,
Emmanuel Korir and
Ferguson Rotich. Five days later, at the
Athletissima in
Lausanne, Arop again defeated Korir and Rotich to claim his second Diamond League gold. Arop's results qualified him to the
Diamond League Final in
Zürich, where he finished in fourth place. Arop began 2022 with this debut at the
World Athletics Indoor Championships at the
2022 edition in
Belgrade. He once again started a race hard and was leading the
800 m at the halfway point, but faded badly down the stretch and finished in eighth place. On the
2022 Diamond League, Arop won his third Diamond League gold, and first of the season, at the
British Grand Prix in
Birmingham. The following month, he won another Canadian national title, besting silver medallist
Brandon McBride by almost a full second. In an invitational event held at
Foote Field weeks before the
2022 World Athletics Championships, he ran the 800 m in 1:43.61, the third-best time for any athlete that year to date. He was second in his semi-final, passed just at the line by Algerian
Slimane Moula, and secured automatic qualification to the final. Looking ahead, Arop said, "it's been a great first two rounds, but if I can't get it done in the final, I won't feel like I completed anything." Racing a 1:44.28 time in the final, Arop won the bronze medal, only the second medal for a Canadian in the 800 m at the World Championships. Arop said this medal "means the world" and was "already looking forward to bigger and better next year." Appearing in the
1000 m event at the
Herculis meet in
Monaco, he set a
new national record time of 2:14.35, breaking a decade-old best of
Nathan Brannen's. Going into the
2023 World Athletics Championships, Arop topped the World Athletics rankings for 800 m runners. He proceeded through the heats by finishing in first place and also won his semifinal heat, leading both from start to finish. In the final, Arop changed strategies and dropped to the back of the pack over the first lap, after 500 m, he moved toward the lead of the pack and did not relinquish first place. Arop was the first Canadian male to win the 800 m at the World Athletics Championships. After the race he said that "my best race plan is to be ready for anything and sometimes that's not having a race plan. When the [start] gun [sounded] my body was telling me to be patient. I've visualized this so many times and seen myself winning, but it doesn't compare to the real thing. I'm still in disbelief and I gotta give a lot of credit to my coach, my support team, my family and everybody behind me." Shortly after his World Championship victory, Arop set a new personal best time of 1:43.24 at the
2023 Xiamen Diamond League event, where he finished narrowly second to Kenyan
Emmanuel Wanyonyi. In the season-ending 2023 Diamond League
Prefontaine Classic he finished second to Wanyonyi again, while setting a new Canadian national record and personal best time of 1:42.85. Arop began his 2024 season on 4 February, competing in the short track 1000 m run at the
New Balance Indoor Grand Prix in
Boston, Massachusetts. Arop won the event in a time of 2:14.74, breaking
Nate Brannen's previous national record in the short track 1000 m of 2:16.87 set back in 2014. Arop missed
Ayanleh Souleiman's short track 1000 m world record of 2:14.20 by only 0.54 seconds, but still set a new North, Central American and Caribbean area record in the event. Prior to the
2024 Olympic Games, on 12 July, Arop competed in the 800 m at the Herculis Meeting in Monaco, finishing sixth in a time of 1:42.93 while Algerian
Djamel Sedjati set a new world lead with a time of 1:41.46. However, after making it through the heats and semifinals, in the
final of the 800 metres at the Games on 10 August, Arop secured a silver medal, finishing second to Kenyan athlete
Emmanuel Wanyonyi, in a new
Canadian national record and new
North, Central American & Caribbean area record of 1:41.20 to become the fourth fastest man in history at the distance. Arop finished only one hundredth of a second behind Wanyonyi, who ran 1:41.19. He finished ahead of Sedjati, who took third place in a time of 1:41.50. On 8 September, at the
Memorial Borisa Hanžekovića in Zagreb, Arop ran a new North American area record in the
1000 m, running 2:13.13 to become the fifth fastest man of all time at this distance. == Competition record ==