Born in Iaşi, he started to study music with his father (an amateur musician). He graduated from the Music Conservatory in Bucharest and became a well-known violinist, performing in concerts all over Romania and also abroad. Having decided to become a conductor, he was granted a scholarship in the field, to École Normale de Musique in Paris, France, where he studied with Charles Münch and Pierre Dervaux. Following that, he studied in the United States with Eugene Ormandy and Leopold Stokowski.
Back in Romania, Ionescu-Galaţi became the conductor of the Philharmonic Orchestra in Braşov. He also conducted many orchestras in Romania and many others from the United States, Japan, People's Republic of China, Italy, France, Germany, Austria, Sweden (he was permanent conductor at Gävle Symphony Orchestra), Russia, Mongolia, Spain, Greece, Turkey (he was the permanent conductor and artistic director at Istanbul State Symphony Orchestra and also permanent conductor at Ankara Symphony Orchestra and Bilkent Symphony Orchestra). He taught conducting classes and violin classes in the United States, Romania, Greece and Turkey.
Ilarion Ionescu-Galaţi played with soloists such as Lazar Berman, Radu Lupu, Fazil Say, Felicia Filip, Daniil Shafran, Igor Oistrakh, Valery Oistrach, Viktor Pikaisen, Rudolf Kerrer, Ion Voicu, Magda Tagliaferro, Idil Biret, Ayla Erduran, Sabine Meyer, Costas Cotsiolis, Aris Garoufalis, Theodore Kerkezos and several others. His discography contains many titles including Gioachino Rossini (all Sei sonate a quattro), Pyotr Ilyich Tchaikovsky (Fifth Symphony), and Antonín Dvořák (Seventh Symphony, with the Tokyo Symphonic Orchestra), Niccolò Paganini, Ludwig van Beethoven, Wolfgang Amadeus Mozart, Camille Saint-Saëns, and Franz Liszt.
After leaving Braşov Philharmonic Orchestra, he became permanent conductor and Honorary Director of the Ploieşti Philharmonic Orchestra. He received medals, honors and assorted prizes and diplomas in Romania, Turkey, Greece and several other countries. In 2008 the pianist Ioana Maria Lupascu wrote a non-fiction book, in which I.Ionescu-Galati is the main character.
- "Despre noi". ORCHESTRA SIMFONICA A FILARMONICII “PAUL CONSTANTINESCU” PLOIESTI. Retrieved 26 September 2011.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>