The World Curling Federation's historical records rank Sundgren as one of the most successful curlers of all time, both in the medals that he has received and his lifetime performance in individual championships.

In 2022, he surpassed the previous record holders for World Men's Curling Championship medals, winning his fifth gold medal, in addition to his and European Men's Curling Championship (5 gold, 2 silver), placing him third of all time on both lists behind his teammates Edin and Oskar Eriksson.

[8] In 2011, Sundgren rejoined his former team in Lit for much of the season while Alexander Lindström was recovering from surgery,[9] helping them finish in first place in Sweden's national Elite Series tour (though coming in second in the finals).

[10] Sundgren played with the team on much the international seniors' tour for the first half of the year and again the end of the season at the European Masters.

[13] With the newly reorganized team, Sundgren and his teammates won the Swiss Cup Basel (2012) and European Masters (2013), as well as the Winter Universiade (2013).

[11] In the 2013-14 season, Team Eriksson reached second place at the Swiss Cup Basel, Mercure Perth Masters, and Sweden's Elite Series and competed in Canada on the World Curling Tour, coming in fifth place in three events and reaching their first Grand Slam Quarterfinal at the National.

Beginning in the 2014–2015 season, Niklas Edin joined forces with Sundgren, Eriksson, and Kristian Lindström to become Sweden's new national team after Sebastian Kraupp and Fredrik Lindberg took a break from full-time curling.

The team also secured medals in the finals of the World Curling Championships every year except 2016, winning three gold (2015, 2018, and 2019) and one silver (2017).

Sundgren, Edin, and Eriksson are also the first curlers in history on the men's side to win four European Championship gold medals in a row (2014-2017).