In 1910, he became an apprentice decorator at the firm Schaijk & Kramers, where Eduard H. Kramers encouraged him to develop his interest in painting, as he had already done for Bram, Geer’s elder brother.
Geer carried out his military service in the Red Cross, then set out on a tour of Flanders on foot, painting signs along the way in order to earn a living and taking advantage of any occasion to paint on location. Entirely self–taught, this adventure was to be his only formal art education.
In 1925 Geer came to live in Paris, where decided to devote himself entirely to painting. His brother Bram was already there, renting an atelier in Bellevue-Meudon, on the outskirts of the city.
In 1933, he married Elisabeth Jokl whom he had met in Montparnasse, and the couple moved to 74, rue de la Glacière in Paris’ 13th arrondissement. In Montparnasse he enjoyed a carefree and bohemian way of life despite rampant poverty.
Between 1929 and 1932, Geer traveled to the south of France, planned a one–man show which he had to abandon for lack of money and instead embarked on a round trip between Paris and The Hague.
Bram and Geer, who were still unsure about what their creative approach would be, displayed their works at the Salon des Indépendants three times, in 1928, 1929 and 1930.
In 1938, thanks to the Irish writer Samuel Beckett, Geer showed 45 paintings at Guggenheim Jeune in London, which was under the direction of Peggy Guggenheim at the time.
Geer then left Paris and settled in Cagnes-sur-Mer where he lived until 1944. He struck up a friendship with Pierre Bonnard, and while there produced many drawings as well as paintings of women in the context of everyday objects: curtains, tables, plants... In 1942, he exhibited his work in Nice.
In 1944, at the news of the liberation, he decided to return to Paris, renting the atelier of Tjerk Bottema, who had died in July 1940, in Cachan, in the suburbs of the city.
In 1946 Geer’s first Paris show at the Galerie Maeght. Aimé Maeght was held, resulting in him receiving a five–year contract from the same. In 1949, the museum in The Hague was to acquire two of his works.
The Elf Tijdgenoten uit Paris (eleven Paris contemporaries) show at the Stedelijk Museum , Amsterdam, February-April 1953 brought together the works of Bazaine, Bossière, Estève, Pignon, Prassinos, Singier, Viera da Silva, Geer and Bram.
In 1953 Geer met the artist Piet Moget, whom Geer would later consider his spiritual master. From 1955, Geer was regularly invited by Piet Moget to show his works in Sweden and at the Rencontres de Port-la-Nouvelle, south of Narbonne, in France.
In 1963, Geer travelled to Brazil for two solo shows: at the Biennale of São Paulo; and another in Rio de Janeiro. After a trip to Ireland, he held another solo show at the Musée Galliéra in Paris and then at Cagnes-sur-Mer and in Amsterdam. His travels later took him to Greece, Algeria and Jerusalem.
In 1973, the Biennale de Cachan opened with a tribute to Geer and Braque.
Geer van Velde died in Cachan, on the 5th of March 1977.
