In 2007–08, Bertāns played for ASK Kadeti II. Between 2008 and 2010, he played for BAA Riga of Latvia's second division. During this time, he also had two stints in the top division with ASK Riga at the end of the 2008–09 season, and with BK Keizarmezs Riga at the start of the 2009–10 season.
After starting the 2010–11 season with BK Barons, in November 2010, Bertāns signed a multi-year deal with Slovenian club Union Olimpija. Following the 2010–11 season, Bertāns was selected by the Indiana Pacers with the 42nd overall pick in the 2011 NBA draft. However, his rights were immediately traded to the San Antonio Spurs along with the rights to 15th overall pick Kawhi Leonard for George Hill.
Partizan
In January 2012, Bertāns left Olimpija and signed a three-and-a-half-year contract with Serbian club Partizan Belgrade. In the Serbian League finals series against Crvena zvezda in June 2013, he tore the ACL in his right knee, which sidelined him for nine months. Bertāns returned to the court on 20 March 2014 against Maccabi Tel Aviv, helping his team get a hard-fought Euroleague Top 16 win against the favoured visitors by contributing two points, two rebounds and one assist in 15 minutes of action. Eight days later, on 28 March 2014, Dāvis scored team-high 20 points in a road EuroleagueTop 16 loss to Lokomotiv-Kuban. Partizan ended the season by winning its 13th and Dāvis' third consecutive Serbian League title, defeating rivals Crvena Zvezda 3–1 in the finals series. On 3 July 2014, Bertāns terminated his contract with the club.
On 19 July 2014, Bertāns signed a three-year contract with Spanish club Laboral Kutxa Baskonia. On 26 March 2015, in a game against Emporio Armani Milano, Bertāns tore the ACL in his right knee, the same injury that sidelined him in 2013. He was subsequently ruled out for six to eight months. Over 22 Euroleague games, he averaged 11.0 points and 2.9 rebounds per game, while also averaging 11.4 points in 25 games of the Spanish League. In Laboral Kutxa Baskonia's very next game following Bertāns' injury, a Spanish League contest versus Valencia BC, each Baskonia player wore Bertāns' number 42 in a show of support for their sidelined teammate. On 14 July 2016, Bertāns and Baskonia agreed on a contract buyout.
On 14 July 2016, Bertāns signed with the San Antonio Spurs. He made his debut for the Spurs in their season opener on 25 October 2016, scoring five points in four minutes off the bench in a 129–100 win over the Golden State Warriors. On 25 November 2016, he set a career high in scoring, pitching in 15 of the Spurs' 56 bench points to help San Antonio defeat the Boston Celtics 109–103. On 7 January 2017, he scored 21 points in a 102–85 win over the Charlotte Hornets. He went 4-of-5 on three-pointers in leading the Spurs in scoring for the first time in 2016–17. On 29 January 2017 against the Dallas Mavericks, Bertāns became just the fourth Spurs rookie with at least 35 three-pointers and 15 blocks in a season, joining Kawhi Leonard, Manu Ginóbili and Lloyd Daniels. On 11 March 2017, he had three three-pointers in a 107–85 win over Golden State to reach 51 three-pointers on the season. He became just the sixth Spurs rookie to hit 50 in a season. During his rookie season, he had multiple assignments with the Austin Spurs of the NBA Development League. Early on the 2017–18 season, Bertāns was twice assigned to the Austin Spurs. On 8 January 2018, he scored a career-high 28 points on 11-of-15 shooting with six 3-pointers in a 107–100 win over the Sacramento Kings. On 13 January 2018, he scored 18 points on a career-high six 3-pointers in a 112–80 win over the Denver Nuggets. On 11 July 2018, Bertāns re-signed with the Spurs for two years and $14 million. On 27 January 2019, he scored a season-high 21 points in a 132–119 win over the Washington Wizards.
Washington Wizards
On July 6, 2019, Bertāns was traded from the San Antonio Spurs to the Washington Wizards in a three-team deal that also included the Brooklyn Nets, in which the Spurs received DeMarre Carroll via sign-and-trade. In his first game in San Antonio following the trade, on 26 October 2019, Bertāns made all seven of his field goal attempts, including five three-pointers, and scored 23 points. On 22 November, he made six three-pointers and scored 20 points against the Hornets. On June 22, 2020, three months into the NBA's hiatus, Bertans decided to pull out of the NBA's Orlando restart; he was the first player to do so. This decision was made due to personal reasons;. Bertans is entering free agency and views sitting out as a preventative measure. Bertans has two previous ACL injuries. If the Wizards don't advance past the seeding games in Orlando, he stands to lose $520,000. The Washington Wizards fully support Bertans' decision and are unlikely to qualify for the playoffs.
National team career
Bertāns represented Latvia at EuroBasket 2011, averaging 5.6 points and 2 rebounds per game. He returned for EuroBasket 2017, now in a more prominent role, averaging 14 points, 3 rebounds and 2 assists per game.
Personal life
Bertāns' older brother, Dairis, is also a professional basketball player; he formerly played for the New Orleans Pelicans. Their father, Dainis, was a professional basketball player and is currently a youth coach. Their mother is a sports teacher and a former high-level rower. Bertāns is fluent in the Serbian language. Due to a childhood wood-cutting accident, Bertāns is missing part of the ring finger on his right hand.
