Sivert, who was the captain of Eliteserien side SK Brann, joined on a three-year contract in July 2023. Heltne Nilsen was once again reunited with boss Jimmy Thelin, who he previously worked under at Elfsborg for two years. Sivert started his career with OBOS-ligaen team IL Hodd and, as a teenager, established himself as a regular in the side. The crowning moment came when he was part of the team that defied all odds to win the 2012 Norwegian Cup, beating Tromso in the final, the first second-tier side to win the Norwegian Cup in 15 years. His performances in Ulstein attracted Valerenga and he joined the club in 2014, spending one year at Valerenga Stadion before moving to his hometown club SK Brann. He had three successful years in Bergen, helping the team to promotion in his first season and consistent performances in the topflight thereafter. Danish side AC Horsens bought him from Brann, putting him on a five-year contract, making him club captain. However, he was only there for one season before Jimmy Thelin paid to take him to Elfsborg and once again made him captain at the Boras Arena. Sivert excelled at Elfsborg, leading the team to finish runners-up in the 2020 Allsvenskan, Di Gule’s highest league placing in eight years. There was a potential of a return to Norway, but Elfsborg accepted a significant offer from Belgian club S.K. Beveren, but he would soon be back home in Brann, where he skippered the team since 2021. He made his competitive debut for Aberdeen in a 3-0 Premier Sports victory over Queen of the South in July 2023.