Seabrooke was born in Upton Park, Essex and studied at the Slade School of Art under Henry Tonks from 1906-11. As a pacifist in WWI he served in the British Red Cross and won Italy's highest award for bravery.
Seabrooke exhibited at the New English Art Club and the London Group, of which he was president in the 1940s. He was initially inspired by the work of Cézanne and later the pointillism of Paul Seurat and painted a series of maritime views in this style - several of which were acquired by the Tate Gallery.