After the war, filled with new ideas, Ernst, Jean Arp and social activist Alfred Grünwald formed the Cologne, Germany Dada group. In 1918 he married the art historian Luise Straus — a stormy relationship that would not last. The couple had a son who was born in 1920, the artist Jimmy Ernst. (Luise died in Auschwitz in 1944.) In 1919 Ernst visited Paul Klee and created paintings, block prints and collages, and experimented with mixed media.

In 1922, he joined fellow Dadaists André Breton, Gala, Tristan Tzara, and Paul Éluard at the artistic community of Montparnasse. Constantly experimenting, in 1925 he invented a graphic art technique called frottage, which uses pencil rubbings of objects as a source of images. He also created another technique called 'grattage' in which paint is scraped across canvas to reveal the imprints of the objects placed beneath. He uses this technique in his famous painting 'Forest and Dove' (as shown at the Tate Modern).

The next year he collaborated with Joan Miró on designs for Sergei Diaghilev. With Miró's help, Ernst pioneered grattage in which he troweled pigment from his canvases. He also explored with the technique of decalcomania which involves pressing paint between two surfaces.

Ernst developed a fascination with birds that was prevalent in his work. His alter ego in paintings, which he called Loplop, was a bird. He suggested this alter ego was an extension of himself stemming from an early confusion of birds and humans. He said that one night when he was young he woke up and found that his beloved bird had died, and a few minutes later his father announced that his sister was born. Loplop often appeared in collages of other artists' work, such as Loplop presents André Breton. Ernst drew a great deal of controversy with his 1926 painting The Virgin Chastises the infant Jesus before Three Witnesses: André Breton, Paul Éluard, and the Painter. In 1927 he married Marie-Berthe Aurenche, and it is thought his relationship with her may have inspired the erotic subject matter of The Kiss and other works of this year. In 1930, he appeared in the film L'Âge d'or, directed by self-identifying Surrealist Luis Buñuel. Ernst began to make sculpture in 1934, and spent time with Alberto Giacometti. In 1938, the American heiress and artistic patron Peggy Guggenheim acquired a number of Max Ernst's works which she displayed in her new museum in London. Ernst and Peggy Guggenheim were also married to one another from 1942 to 1946.

In 1938 he was interned in Camp des Milles, near Aix-en-Provence, along with fellow surrealist, Hans Bellmer, who had recently emigrated to Paris on the outbreak of World War II. Thanks to the intercession of Paul Éluard, and other friends including the journalist Varian Fry he was discharged a few weeks later. Soon after the Nazi occupation of France, he was arrested again, this time by the Gestapo, but managed to escape and flee to America with the help of Guggenheim. He left behind his lover, Leonora Carrington, and she suffered a major mental breakdown. Ernst and Guggenheim arrived in the United States in 1941 and were married the following year. Along with other artists and friends (Marcel Duchamp and Marc Chagall) who had fled from the war and lived in New York City, Ernst helped inspire the development of Abstract expressionism.

His marriage to Guggenheim did not last, and in Beverly Hills, California in October 1946, in a double ceremony with Man Ray and Juliet P. Browner, he married Dorothea Tanning. The couple first made their home in Sedona, Arizona. In 1948 Ernst wrote the treatise Beyond Painting. As a result of the publicity, he began to achieve financial success.

In 1953 he and Tanning moved to a small town in the south of France where he continued to work. The City, and the Galeries Nationales du Grand-Palais in Paris published a complete catalogue of his works.

In 1966 he created a chessgame made of glass which he named "Immortel"; it has been described by the poet André Verdet as

a masterpiece of bewitching magic, worthy of a Maya palace or the residence of a Pharaon.

Ernst died on 1 April 1976, 1 day before his birthday, in Paris. He was interred at the Père Lachaise Cemetery.

Max Ernst's life and career are the subject of Peter Schamoni's 1991 documentary Max Ernst. Dedicated to the art historian Werner Spies, it was assembled from interviews with Ernst, stills of his paintings and sculptures, and the memoirs of his wife Dorothea Tannning and son Jimmy. The 101-minute German film was released on DVD with English subtitles by Image Entertainment.

In 2005, "Max Ernst: A Retrospective" opened at the Metropolitan Museum of Art and included works such as Celebes (1921), Ubu Imperator (1923), and Fireside Angel (1937), which is one of the few definitively political pieces and is sub-titled The Triumph of Surrealism depicting a raging bird-like creature that symbolizes the wave of fascism that took over Europe. The exhibition also includes Ernst's works that experiment with free association writing and the techniques of frottage, created from a rubbing from a textured surface; grattage, involving scratching at the surface of a painting; and decalcomania, which involves altering a wet painting by pressing a second surface against it and taking it away.

Ernst's son Jimmy, a well known German/American abstract expressionist painter, who lived on the south shore of Long Island, died in 1984. His memoirs, A Not-So-Still Life, were published shortly before his death. His grandson Eric and granddaughter Amy are both artists and writers.