Early career

Dieck started skating in 2000 and took up ice dancing in 2011.^[3] He skated with Dana Wehner in the 2011–12 season. They placed ninth at the 2012 German Junior Championships.^[5]

In 2012–13, Dieck began competing with Florence Clarke. They were fifth at the 2013 German Junior Championships. The following season, they debuted on the ISU Junior Grand Prix series, finishing ninth in Riga, Latvia and fifteenth in Gdańsk, Poland. They were also assigned to the 2014 World Junior Championships in Sofia, Bulgaria, but were eliminated after placing twenty-seventh in the short dance.^[6] Clarke decided to retire at the end of the season.^[7][8]

2014–15 season

Vitali Schulz arranged a tryout between Dieck and Katharina Müller.^[8] They teamed up in April 2014, coached by Schulz und James Young in Dortmund.^[3] Assigned to two Junior Grand Prix events, they placed eighth in Ljubljana, Slovenia, and seventh in Aichi, Japan. After winning the 2015 German junior national title, they were sent to the 2015 World Junior Championships in Tallinn, Estonia; ranked thirteenth in the short dance, they qualified for the final segment and finished twelfth overall.

2015–16 season

Competing in the Challenger Series (CS), Müller/Dieck finished tenth in September at the 2015 Nebelhorn Trophy – their first senior international – and eighth the following month at the 2015 Mordovian Ornament. In November, they won bronze at the 2015 NRW Trophy before appearing at their third CS event, the 2015 Tallinn Trophy, where they placed fifth. They were awarded the silver medal at the German Championships in December, having finished second to Lorenz/Polizoakis, and took bronze at the Toruń Cup. Müller/Dieck were included in Germany's team to the 2016 European Championships in Bratislava, Slovakia, but were eliminated after placing twenty-third in the short dance.^[9]

In spring 2016, Müller/Dieck began training under Marina Zueva in Canton, Michigan, in addition to Schulz and Young in Dortmund.^[3]

2016–17 season

Müller/Dieck competed at two Challenger events, placing twelfth at the 2016 CS U.S. Classic and ninth at the 2016 CS Nebelhorn Trophy. They won gold at the NRW Trophy for the first time, and were the German national silver medalists for the second consecutive year.^[10]

2017–18 season

Competing three times on the Challenger series, Müller/Dieck were fifth at the 2017 CS Warsaw Cup, sixth at the 2017 CS Ice Star, and eleventh at the 2017 CS Golden Spin of Zagreb. They won the silver medal at the German championships for the third consecutive year.^[10]

2018–19 season

Again competing on the Challenger series three times, Müller/Dieck were seventh at both the 2018 CS Nebelhorn Trophy and the 2018 CS Golden Spin of Zagreb and ninth at the 2018 CS Ondrej Nepela Trophy. They were invited to make their Grand Prix debut, placing seventh at the 2018 Skate America and tenth at the 2018 Grand Prix of Helsinki. NRW Trophy champions for the second time, they then won their fourth consecutive silver medal at the German championships.^[10]

2019–20 season

Müller/Dieck's three Challenger competitions for the year were the 2019 CS Ondrej Nepela Memorial, the 2019 CS Ice Star and the 2019 CS Golden Spin of Zagreb, where they placed eighth, sixth and sixth, respectively. They did not return to the Grand Prix, but won the inaugural Denis Ten Memorial Challenge and the Open d'Andorra, followed by becoming German national champions for the first time.^[10]

Müller/Dieck attended the European Championships for the first time in four seasons, placing thirteenth.^[10] They were supposed to make their World Championship debut at the 2020 edition in Montreal, but these were cancelled as a result of the COVID-19 pandemic.^[11]

2020–21 season

Despite the continued limitations of the pandemic on international competition, Müller/Dieck won their first Challenger medal, a silver at the 2020 CS Budapest Trophy, as well as their third gold medal at the NRW Trophy. Repeating as German national champions, they went on to make their World Championship debut at the 2021 World Championships in Stockholm, where they came in eighteenth.^[10] This result qualified a berth for a German ice dance team at the 2022 Winter Olympics in Beijing.^[12]

2021–22 season

Müller/Dieck began the season at the 2021 CS Nebelhorn Trophy, winning the silver medal. Dieck noted that it was "always special to win a medal in Germany," while Müller said, "we were not competing for an Olympic spot here, but it was important to us for our national qualification and to prove that we are ready and want to go to the Olympic Games."^[13] They came ninth at the 2021 CS Finlandia Trophy.^[10]

Initially assigned to the 2021 Cup of China on the Grand Prix, upon its cancellation Müller/Dieck were reassigned to the 2021 Gran Premio d'Italia.^[14] They finished in eighth place.^[15] They were sixth at the 2021 CS Cup of Austria and second at the Open d'Andorra.^[10]

Despite losing the German national title to rivals Janse van Rensburg/Steffan, Müller/Dieck were named to the German Olympic team. They first competed at the 2022 European Championships, finishing in twelfth place.^[10]

Müller/Dieck began the 2022 Winter Olympics as the German entries in the rhythm dance segment of the Olympic team event, where they finished tenth among ten.^[16] In the dance event, they were twenty-first in the rhythm dance, missing the cut for the free dance.^[17]

The team encountered new difficulties following the Olympics, as Vladimir Putin's invasion of Ukraine and resultant tensions between Russia and Germany resulted in their being unable to return to their Moscow training location.^[18] Dieck and Müller later separated.^[19]

2023–24 season

Following the end of his partnership with Müller, Dieck connected with Anglo-Spanish ice dancer Olivia Smart. The two explored representing either Germany or Spain, but the Spanish Ice Sports Federation offered superior financial support and they requested Dieck be released by the German Ice Skating Union.^[20] The release was granted in December 2022, and it was announced that they would begin training in April 2023 in Montreal under Smart's longtime coaches Marie-France Dubreuil, Patrice Lauzon and Romain Haguenauer.^[19]

Smart/Dieck made their international competitive debut at the 2023 CS Autumn Classic International, coming fourth. They went on to finish fourth as well at the 2023 CS Finlandia Trophy.^[21] Making their Grand Prix debut as a team at the 2023 Skate America, Smart/Dieck placed sixth.^[22] They were then eighth at the 2023 Grand Prix de France.^[23]

Competing at their first Spanish Championships in December, Smart/Dieck won the gold medal over rivals Val/Kazimov.^[24] Despite this, it was initially announced by the Spanish federation that Val/Kazimov would represent the country at the 2024 European and World Championships. Following controversy around the criteria used to arrive at this result, on December 27 the Spanish federation announced that Smart/Dieck would instead be given the country's lone World Championship berth.^[25][26]

Smart/Dieck won the silver medal at the International Challenge Cup in February.^[21] At the World Championships, held in Montreal, the home of the team's training base, Smart/Dieck were fifteenth in the rhythm dance and qualified to the free dance.^[27] An error on their dance spin saw them finish twentieth among twenty teams in the free dance, dropping to nineteenth overall. Smart remarked that the mistake "fits within this season full of ups and downs, which we accept as a lesson we have to learn"^[28]

With Smart

With Müller

With Clarke

With Smart for Spain

With Müller for Germany

With Clarke for Germany

With Wehner for Germany

With Smart for Spain