Agdestein started his career at Stord IL, playing 35 games and scoring 16 goals.
Brighton & Hove Albion
In 2010, Agdestein was transferred to English club Brighton & Hove Albion for an undisclosed fee and featured in the development squad. Agdestein made his first competitive appearance for Brighton during an FA Cup 3rd round replay against Wrexham. Three days later, he made his first league appearance for Brighton coming on as a second-half substitute and providing an assist to Will Buckley in a 2–1 victory at Peterborough United. Towards the end of the 2010–11 season, Agdestein had his Brighton contract extended for one-year. During September 2011, Agdestein joined Conference National side Bath Cityon loan. However, making three appearance, Agdestein returned to Brighton. Following his return from Bath City, Agdestein soon played regularly in the reserve team and in March 2012, signed a two-year contract. On 26 July 2013, Agdestein left Brighton after his contract was terminated by mutual consent despite having one-year left to run.
Agdestein signed for Inverness CT in July 2013 on a six- month contract, the club beating off competition from Viking. However, Agdestein suffered a lack of playing time due to the form of Billy McKay and only made one start. Despite a desire to sign a new contract, Agdestein left the club when his contract expired and his agent said he was in talks with English clubs.
After leaving Scotland and not getting a move to England, Agdestein returned to Norway, where he joined Tippeligaen side Haugesund. On 30 March, he signed a loan deal with OBOS-ligaen club Kristiansund. After breaking into the first team squad he earned the title as the club's top goalscorer in his final Haugesund season after bagging 10 league goals.
Odd
He signed for Odd on the 17 August on a three year deal. Agdestein only earned 7 league appearances and failed to score a single league goal. He did, however, score a hat-trick against IL Hei in the first round of the 2017 Norwegian Football Cup.
Aalesund
Before the 2018 season he signed for OBOS-ligaen side Aalesunds FK on a three year deal.
