BC Žalgiris-2 and debut in the LKL (2014–2017) Birutis began his professional career when he signed with
BC Žalgiris-2 in the summer of 2014. On 5 January 2016, he set a
National Basketball League record with 23 rebounds in a game against
BC Petrochema. Later that season, he won silver medals with Žalgiris-2 after losing the final game against
BC Sūduva. On 14 April 2017, after dominating the second-tier National Basketball League by averaging 17.4 points, nine rebounds, 1.4 assists and two blocks per game, Birutis was invited to join
Vytautas Prienai–Birštonas in the top-tier
Lithuanian Basketball League. Birutis made a strong debut on 15 April 2017, scoring 17 points and grabbing four rebounds, but his team lost 92–89 after
Justas Tamulis buzzer-beater. Two days later, he recorded his first LKL win 96-89 against
Neptūnas Klaipėda and was the second-best Vytautas' scorer with 19 points and six rebounds.
BC Šiauliai (2017–2018) On 1 August 2017, Birutis was loaned his hometown club
BC Šiauliai. During the
2018 Karaliaus Mindaugo taurė quarterfinals against the Lithuanian champions
Žalgiris Kaunas, Birutis played the best game of his career by scoring 35 points, grabbing 11 rebounds, dishing out 2 assists and blocking one shot, although his team lost 85–78. On 18 April 2018, Birutis entered his name into the
2018 NBA draft. During his second LKL season, he led the league in all three major statistical categories of his position, with 14.9 points, 7.3 rebounds and 1.3 blocks. For his performances throughout the campaign, Birutis received the
LKL Most Valuable Player Award. Furthermore, with his help, BC Šiauliai recovered from the league's worst record last season (6–30) and became a solid playoff participant by finishing fifth in the regular season (16–20). At the season closing ceremony he was also named the LKL Best Young Player. It was also announced that Birutis would return to Žalgiris for the 2018–19 season.
Žalgiris Kaunas (2018–2019) Birutis joined Lithuanian champions Žalgiris Kaunas and made his
EuroLeague debut on 12 October 2018 against
Saski Baskonia. He scored seven points in 10 minutes. Birutis struggled with injury since the start of the season and was unable to train due to pain, which led to surgery on 14 February 2019. On 1 June, he won his first LKL championship.
CBet Prienai (2019–2020) For the 2019–20 season, Birutis was loaned to
CBet Prienai. On November 23, he made his return to the court, scoring nine points and four rebounds in 16 minutes, including the game-winning shot, in a thrilling 81–79 win over
BC Pieno žvaigždės. He was later named LKL Player of the Month for February. He had his best game on 1 February 2020 against BC Neptūnas, in which he scored 25 points and collected 36 efficiency points. He finished the 2019–20 LKL season as the league leader in efficiency, averaging 20.4
PIR per game. Additionally, he ranked second in the league in both scoring and rebounding with 15.2 points and seven rebounds per game.
Monbus Obradoiro (2020–2022) On July 24, 2020, Birutis signed a two-year contract with
Monbus Obradoiro of the Spanish
Liga ACB. On 28 September 2020, Birutis was named Liga ACB
MVP of September after averaging 19.3 points, 8 rebounds and 1 block per game.
Žalgiris Kaunas (2022–present) On 10 June 2022, Birutis returned to
Žalgiris Kaunas, signing a two-year deal. He was named to the All-LKL Team for two consecutive seasons, in 2023 and 2024. On 9 April 2024, Birutis signed a contract extension through 2026. ==National team career==