A holding midfielder,[3] Oksanen began his career in his native Finland as a youth with KP-75 and KOPSE, before entering the academy at Veikkausliiga club HJK Helsinki at the age of 12.

[8] One week after the playoff victory, Oksanen made his senior debut for HJK Helsinki, as an 81st-minute substitute for Evans Mensah in a 3–2 defeat to RoPS on 28 October 2017.

[4][5] On 13 January 2018, Oksanen moved to England to sign for the B team at Championship club Brentford on a 2+1⁄2-year contract for an undisclosed fee.

[19] On 31 August 2021, Oksanen joined Scottish Championship club Greenock Morton on loan until 3 January 2022 and made 16 appearances during his spell.

[9][34][35][36][37] He appeared in each of Finland's three matches at the 2018 European U19 Championship and his development during 2018 was recognised with the SPL Most Promising Young Player of the Year award.

[5][38] Oksanen won his maiden call into the full Finland squad for a January 2022 training camp in Algarve, which included two friendly matches.