He studied painting at the School of Fine Arts in Buenos Aires, Argentina between 1947 and 1951, under the tutelage of Jorge Soto Acebal.
As a painter he worked light in collage and mixed media applied by bright colors.
He began his career using semi-abstract references to urban congestion, as well as fish, insects and other animals.
In spite of the fact that the Panamanian public did not understand much of his art, in 1955 he was awarded a prize for a piece that included bits of glass.
With the passage of time Sinclair's painting followed the lines of a lyrical abstraction that went from collages to soft and luminous compositions.