During his early career aged 14, Sedekerskis played for
Kuršiai Neringa in the third-tier Lithuanian basketball league –
RKL, averaging 10.6 points, 3.8 rebounds and 1.8 assists per 27 minutes over 5 games in the 2012–13 season. In June 2013, Sedekerskis signed a "1+2+3" contract with
Baskonia of Spain. On May 10, 2014 Sedekerskis led Baskonia's junior team to a bronze medal after scoring 34 points (2-pointers: 7/10, 3-pointers: 4/11, FT: 8/11), grabbing 10 rebounds and making two steals. At the age of only 17, he debuted in
Baskonia's men's team during a
Liga ACB win against
Joventut Badalona by 87–68. in the
2022–23 EuroLeague season He tallied four points and a team-high five rebounds as a member of the World Select Team at the 2017
Nike Hoop Summit. On September 1, 2017, Sedekerskis extended his contract with
Baskonia until 2022 and went on loan to
San Pablo Burgos for the 2017–18 season. On December 16, 2017, Sedekerskis end his loan with San Pablo Burgos after appearing inconspicuously in eight games with Spanish club and went on loan to
Nevėžis of the
Lietuvos krepšinio lyga. In April 2019, he declared for the
2019 NBA draft. On July 26, 2019, Baskonia loaned him to
Neptūnas for the 2019–20 season. On July 27, 2021, Sedekerskis signed a contract extension with Baskonia until the end of the 2023–24 season. During the 2023-24 campaign, he was named
team captain after the departure of fellow Lithuanian
Rokas Giedraitis. On March 4, 2024, Sedekerskis renewed his contract with the club through 2029. ==National team career==