Junior level: 2005–2010 Stefanidi attended the 1st High School of
Pallini where she won the National High School Championships. She broke the national high school
pole vault record and the championship record, winning gold at the 2006
Gymnasiade. Growing up she broke all of the world age-group records for the ages of 11–14 and right after she turned 15, she broke the world under-18 best with a jump of 4.37 m. Her first international experience came at the age of 15, when she represented Greece at the
2005 World Youth Championships in
Marrakesh, winning the gold medal and setting a championship record of 4.30 m in the process. At the
2007 edition held in
Ostrava, she was second with 4.25 m. In 2008, the 18-year-old won the bronze medal with 4.25 m at the
World Junior Championships in
Bydgoszcz, Poland. The same year, she gained an
athletic scholarship at
Stanford University and began competing for the
Stanford Cardinal track and field team. She received her master's degree in
cognitive psychology with Dr. Gene A. Brewer at
Arizona State University while training under the guidance of 2000 Olympic pole vault champion
Nick Hysong. At Stanford, Stefanidi broke the freshman school record with a leap of 4.13 m, under the guidance of coach Kris Mack and head coach
Edrick Floreal. In 2010, under the guidance of
Toby Stevenson, she tied for fifth place (4.30 m) at the
NCAA Division I Indoor Championships, was the
Pac-10 Conference champion and tied for fourth (4.25 m) at the
NCAA Division I Outdoor Championships, after breaking the school record multiple times.
2011–2013 In 2011, she was second at the NCAA Indoors with 4.40 m. That same year she defended her Pac-10 Conference title (4.28 m) and was third at the
NCAA Outdoors with 4.40 m. She placed second at the
European Under-23 Championships in
Ostrava, Czechia and third at
Universiade in
Shenzhen, China, after jumping a personal best of 4.45 m in both competitions to tie the Greek U23 record. Her senior year, Stefanidi placed third at the NCAA Indoors (4.35 m). In the 2012 outdoor season, she was again the Pac-12 Conference champion in
Eugene, Oregon, where she broke her own school record with 4.48 m. A month later she became the NCAA champion in
Des Moines, Iowa, clearing 4.45 m. Her season's best, 4.51 m, achieved in July in
Livermore, California, is the Greek under-23 record. In 2013, she faced some injury problems, thus not improving her personal best, with a 4.45 m season's best.
2014–2015 in
Zurich In the 2014 indoor season, she improved her personal best to 4.55 m. In the 2014 outdoor season, she improved her lifetime best to 4.57 m and then established even better best of 4.60 m at the
Diamond League meeting in
New York City. She competed for the first time at the European Athletics Team Championships 1st league, held in
Tallinn, representing Greece and winning with a 4.55 m jump. She managed to improve her PB again at the
Glasgow Diamond League in with a jump at 4.65 m. One week before the European Championships she set another personal best at 4.71 m, equaling the
Greek national record. At the
2014 European Championships held in
Zurich, Switzerland she had an easy qualification, while in the final she had her first success in major events by winning the silver medal with 4.60 m, losing the gold medal in the very last jump of the event to
Anzhelika Sidorova. She later won the
Birmingham Diamond League meeting with 4.57 m and took the third place at the circuit's final held in
Zürich with 4.67 m. With these results, she took the second place overall at the Diamond League series, only behind
Fabiana Murer. During 2014, she jumped 10 times above 4.55 m, while her pre-2014 PB was 4.51 m. During the 2015 indoor season, she set a personal best four times (4.56 m, 4.60 m, 4.61 m and 4.77 m, which was temporarily the national record). At the
2015 European Indoor Championships, she won the silver medal with 4.75 m. In the 2016 indoor season, she set a national record with a huge leap of 4.90 m at the
Millrose Games, which ranked her at
fourth place of all time in the event, tied with
Demi Payne who cleared the same height at the same meeting. At the
World Indoor Championships in
Portland, Oregon, Stefanidi won the bronze medal with a jump of
4.80 m. In the following months she continuously improved her personal outdoor record (4.73, 4.75 and 4.77 m), and in
Filothei, she set a Greek record of 4.86 m. In July at the
Amsterdam European Championships, she won the gold medal with 4.81 m, taking the competition record from
Yelena Isinbayeva. At the
2016 Rio Olympics, Stefanidi became Olympic champion with a jump of 4.85 m, becoming the seventh Greek female athlete to win a gold medal at the
Summer Olympic Games. In September, she won her first
Diamond League Trophy.
2017–2018 During the 2017 indoor season, she became the
European Indoor champion with a world-leading jump of 4.85 m. In the 2017 summer season, she set a world lead at the
Rome Diamond League with 4.85 m and attempted for the first time to set a new world record. Two years after a disappointing performance at the
2015 Beijing World Championship, where she missed the final, Stefanidi won the gold medal at the
World Championships held in London, where she even broke her own Greek record and set a new world lead for 2017 by vaulting 4.91 m. Katerina completed her 2017 outdoor season undefeated (14 wins in a row) and winning the Diamond League final in
Brussels. On 14 October that year, at the traditional
European Athletics gala in
Vilnius, Lithuania, she was named
European Women's Athlete of the Year. She was training at SPIRE Institute and Academy to prepare for the
2020 Tokyo Olympics. At the Games, she took the fourth place, equaling her season's best with a jump of
4.80 m. In 2022 Stefanidi won the silver medal at the European Championships in Munich, behind
Wilma Murto, with a season's best (4.75m). In 2024 she took the second place at the European Championships in Rome (4.73m). ==Achievements==