Raised in Spain from age six, Rațiu progressed through the Villarreal youth academy, but did not make his debut for the first team. After a loan spell at Dutch club ADO Den Haag between 2020 and 2021, he moved to Huesca. Two years later, he transferred to Rayo Vallecano, with which he registered his La Liga debut.
Rațiu made his senior international debut for Romania in September 2021, in a 2–0 win over Iceland. He represented the country in the UEFA Euro 2024.
After being regularly used with the C-side, Rațiu made his debut for the reserves on 17 December 2017, replacing Darío Poveda late into a 3–2 home win against Peña Deportiva in the Segunda División B championship.[5] He was definitely promoted to the B-team in August 2018,[6] being regularly used afterwards. He made his first team debut the following 18 April, starting in a 2–0 derby loss at Valencia for the season's UEFA Europa League.[7]
On 4 August 2020, Rațiu was loaned to Dutch Eredivisie side ADO Den Haag for the campaign.[8] He returned to his parent club the following 29 January, after 12 appearances.[9]
On 26 August 2023, Rațiu agreed to a five-year deal with La Liga side Rayo Vallecano.[11] He made his debut on 1 November, in a 6–0 Copa del Rey thrashing of Atlético Lugones in which he also scored.[12] Four days later, he played the full 90 minutes in a goalless league away draw at Real Madrid.[13]
In 2023, Rațiu made five appearances in the Euro 2024 qualifiers, which included a start in the final 1–0 victory over Switzerland. Romania emerged as Group I winners, maintaining an undefeated record throughout.[16] On 7 June 2024, he was chosen by Edward Iordănescu in the squad for the final tournament.[17] Rațiu started in all four matches, as the nation won its group but was eliminated by the Netherlands in the round of 16.[18] His blue-dyed hair during the tournament led to him being nicknamed "Sonic", inspired by Japanese character Sonic the Hedgehog.[19][20]