[6] In 2009, Girgensons moved to North America and played in the Eastern Junior Hockey League (EJHL) for the Green Mountain Glades.

He had a slow start to the season and, at the beginning of 2013, he suffered an injury from a late hit by Richard Pánik of the Syracuse Crunch.

He scored his first career NHL goal in the Sabres' season opener against Jimmy Howard of the Detroit Red Wings on 2 October 2013.

On 4 January 2021, a day before his 27th birthday, Girgensons sustained a lower-body injury during a training camp scrimmage ahead of the 2020–21 NHL season and had to be helped off the ice.

He was promptly signed to add forward centre depth on a three-year, $2.55 million contract with the Tampa Bay Lightning.

He made his senior national team debut in 2013 World Championships against the United States and scored his first international goal against Slovakia.

[26][27][28] On 7 January 2014, it was announced that Latvia head coach Ted Nolan had included Girgensons on his national team roster for the 2014 Winter Olympics.

His father, Aldis Girgensons, played as defenceman for RTU Hanza Riga,[31] and is the general manager of East Hokkaido Cranes of the Asia League Ice Hockey (ALIH) and led the team to victory in the All-Japan Championship in December 2020.