Omar Onsi was a pioneer of modern painting in Lebanon and is considered Lebanon's most renowned landscape painter along with Mustapha Farroukh
Onsi was born in Beirut. After an attempt to study medicine, Onsi studied painting in Beirut with Khalil Saleeby.
From 1922 to 1927, he traveled to Transjordan, where he taught painting and English to the children of King Abdullah. The discovery of the desert and its colours during this stay had a major influence on his work.
In 1928, Onsi went to Paris to continue his training and stayed for 3 years, attending the Académie Julian and different workshops. During that period, Onsi focused on painting portraits, nudes, and Parisian scenery.
In 1933, he returned to Lebanon, bringing back a colorful impressionist palette and a French second wife. From then on, his work focused on the Lebanese landscape.