Born in Oss,[2] Oratmangoen turned professional with NEC in April 2016.[3] In December 2017 he signed a six-month loan contract with TOP Oss, effective from January 2018.[4]
Cambuur
After Oratmangoen had been demoted to the reserve team Jong NEC as a result of fierce competition in his position ahead of the 2019–20 season, he moved to SC Cambuur on a free transfer on 24 July 2019. There, he signed a two-year contract with an option for another season.[5] He then signed with Go Ahead Eagles in May 2021, who had also won promotion to the Eredivisie.[6]
Groningen
On 15 April 2022, Oratmangoen signed a three-year contract with a two-year option with Groningen, starting from the 2022–23 season.[7]
On 13 August 2024, Oratmangoen officially joined Belgian Pro League club F.C.V Dender on a two-year contact.[9] Oratmangoen made his debut for the club on 22 September 2024, against Genk in a 0–4 defeat.[10] On 26 October 2024, Oratmangoen scored his first league goal for Dender in a 2–5 home loss to Mechelen.[11]
International career
In November 2023, Oratmangoen confirmed that he had decided to represent Indonesia at international level.[12] On 7 March 2024, Oratmangoen was called up to the Indonesia national team for the 2026 FIFA World Cup qualification matches against Vietnam.[13] On 26 March 2024, Ragnar scored in his debut against Vietnam in a 3–0 win, earning the man-of-the-match for his performance.[14][15]
On 5 September 2024, Oratmangoen gave an assist towards Sandy Walsh deflection against Saudi Arabia in a 1–1 draw in the third round of World Cup qualifiers. On 10 October 2024, Oratmangoen scored against Bahrain, in a controversial match that ended in a 2–2 stalemate.[16]