Duplantis was born into an athletic family; his American father, Greg Duplantis, is a former pole vaulter with a personal best of 5.80 m, while his Swedish mother Helena is a former heptathlete and volleyball player. His two older brothers, Andreas and Antoine, also took up sports; Andreas represented Sweden as a pole vaulter at the 2009 World Youth Championships and 2012 World Junior Championships, while Antoine dropped pole vault for baseball in high school before heading to Louisiana State University where he became the team's career hits leader in 2019. Armand Duplantis first tried pole vaulting as a three-year-old at the family's home in Lafayette, Louisiana, and took to the event rapidly; he set his first age group world best at age 7, and his jump of 3.86 m as a ten-year-old surpassed the previous world bests for ages 11 and 12 as well., he holds the world best in all age groups from age 7 to age 12; he held the age 13 record until it was broken in May 2015.
2015
In 2015, his freshman year at Lafayette High School, Duplantis set national freshman records both indoors and outdoors and was named Gatorade Louisiana Boys Track & Field Athlete of the Year. As a citizen of both the United States and Sweden, Duplantis could have chosen to vault for either country internationally; in June 2015 it was announced that he had selected Sweden. Duplantis represented Sweden for the first time at the 2015 World Youth Championships in Cali, Colombia; he won gold on countback with a first-attempt clearance of 5.30 m, improving his personal best by two centimeters and setting a new championship record.
2016
Duplantis cleared 5.49 m at a high school meet in Baton Rouge on 6 February 2016, setting a new age 16 world best, world indoor youth best and national high school indoor record; he was the first high school athlete to vault 18 feet indoors. Emmanouil Karalis of Greece, the same age as Duplantis, broke his world marks with a 5.53 m jump only one week later.
2017
On 11 February 2017, at the Millrose Games, Duplantis jumped to set the World Indoor Junior Record. That mark was ratified by IAAF. A month later he improved to 5.82 m in the same facility at the New Balance National Scholastic Championships. That mark was not ratified due to incorrect peg lengths being used. On 1 April 2017, Duplantis jumped 5.90 m at the Nike Clyde Littlefield Texas Relays, improving his personal record and setting a new World Junior Record. The jump also became a Swedish senior record by 3 cm. While the IAAF recognized the record with Duplantis representing Sweden, on 2 December 2017, USATF also ratified Duplantis' mark as the American Junior record.
2018
Duplantis began his 2018 season by improving upon the World Indoor Junior Record by jumping 5.83 at the Pole Vault Summit in Reno, Nevada. He later improved his indoor record to and reached at the 2018 European Athletics Championships. The 6.05 ranked him tied as the No. 5 pole vaulter in history and tied for No. 2 outdoors.
On 4 February, Duplantis cleared 6.00 m indoors at his first competition of the season. He followed that up with three attempts at a new world record of 6.17 m. On his second attempt, he cleared the bar but brushed it off with his arm on the way back down. On 8 February, Duplantis broke Renaud Lavillenie's almost 6 year old world record with a jump of 6.17 m in Toruń, Poland. A week later, on 15 February in Glasgow, he increased the record by another centimetre to 6.18 m. On 19 February, Duplantis won the Meeting Hauts de France Pas de Calais by clearing 6.07 m, after which he made three unsuccessful attempts at the new world record height of 6.19 m. A few days later, on 23 February, Duplantis won the All Star Perche in Clermont-Ferrand by clearing 6.01 m in his last indoor competition for the season which ended with new unsuccessful attempts at 6.19 m. On 14 July, he received a scholarship from Swedish Crown Princess Victoria.
