[4][5][6] He made his Divizia A debut, playing for Rapid București under coach Ion Mihăilescu on 30 October 1960 in a 2–0 loss in front of Minerul Lupeni.

[4][5][6] In the 1966–67 season, under the guidance of coach Valentin Stănescu he helped Rapid win the first league title in the club's history, being the team's top-goalscorer with 15 goals scored in 22 matches.

[4][5][8][9] In the following season he appeared in four matches in the 1967–68 European Cup campaign, scoring one goal against Trakia Plovdiv which helped Rapid advance to the following round where they were eliminated by Juventus.

[4][5][6][15][16] After two years spent in West Germany at Alemannia Aachen, Ionescu came back in Romania to play for Crișul Oradea where he made his last Divizia A appearance on 28 June 1970 in a 0–0 with Dinamo Bacău, having a total of 184 matches in which he scored 107 goals in the competition.

[4][5] Ion Ionescu played 15 games at international level for Romania, making his debut on 23 December 1962 when coach Silviu Ploeșteanu sent him on the field at half-time to replace Cicerone Manolache in a friendly which ended with a 3–1 loss against Morocco.