Gerard Jozef Portielje was a Belgian painter of genre scenes.

He was born in Antwerp, the son of painter Jan Portielje. His younger brother, Edward, was also a painter. He attended a trade school until 1870, then entered the Royal Academy of Fine Arts. His teachers included Polydore Beaufaux, Jozef Van Lerius and Edward Dujardin.

In 1887, he took a study trip to Vosges and Alsace. In 1898, he visited England and spent some time at Lowestoft. When World War 1 broke out, he returned to England, via Ostend and spent the war years in Worcester Park, Surrey where he produced many landscapes and portrayals of country houses.

For some unknown reason, he did not participate in exhibitions of Belgian artists in exile that were given at Kingston upon Thames and Oxford in 1915. He and his family returned to Belgium in 1919.

From 1898 to 1914 he was an art teacher at the church school on Lange Leemstraat in Antwerp. He took up that position again in 1919 and remained until 1925. He was also a Professor of Drawing at the Antwerp Academy. He died in 1929 in Remich.