Ognjen Jaramaz began his professional career with Mega from Belgrade, for which he also played in the ABA League in the 2014/15 season, and he gained his first international experience in the 2018/19 season in Spain, where he wore the jersey of San Pablo Burgos. That same season, he returned to Serbia, where he put on the Partizan jersey. He remained with the Black-and-Whites until 2021, when he moved to Bayern Basketball, and in the 2023/24 season he returned to Partizan. He spent the 2024/25 season with Baskonia, and then in the 2025/26 season he played for Ilirija, which he joined at the end of October. In the EuroLeague, Jaramaz has played a total of 105 games, and so far 26 in the EuroCup. Jaramaz can also boast three Serbian Cup titles and the 2019 ABA League Supercup title. In 2017, he was also selected in the NBA Draft by the New York Knicks as the 58th overall pick.

He wore the jersey of the Serbian senior national team at EuroBasket 2022, where he played in six games and averaged 6.3 points and 2.2 rebounds per game, as well as in the 2019 World Cup Qualifiers, EuroBasket 2022 and 2025 Qualifiers, and the 2023 World Cup Qualifiers. With the Serbian U20 national team, he won two medals – gold in 2015 in Italy, and a year earlier bronze in Greece.

In the 2025/26 season, he appeared in four games of the AdmiralBet ABA League for Ilirija – he spent an average of 29.0 minutes on the court, during which he averaged 11.0 points, 5.5 assists, and 3.0 rebounds per game.