His first major success came in 1923 with renowned actor-director Charles Dullin's staging of his play Voulez-vous jouer avec moâ? (Would You Like to Play with Me?), a sensitively delicate comedy about circus and its clowns. The play set a pattern for the remainder of his plays, most of which can be considered as 20th century reworkings of stock characters and situations from the Italian traditional Commedia dell'arte. The personages of Pierrot and Columbine are transported into modern-day settings and inserted into an occasionally mawkish or nostalgic love plot with equal doses of laughter mingled with pain and regret.
These themes were expanded upon in two of his most popular plays of the period—1929's Jean de la Lune (John of the Moon a/k/a The Dreamer) and 1932's Domino. Jean showed how the unwavering trust of Jef, the faithful Pierrot prototype, transforms his scandalously adulterous wife into his idealized image of her, while Domino presented another unfaithful wife who pays a gigolo to make a pretense of courting her so as to distract her husband from her real lover, but the gigolo manages to act his character with such pretend sincerity that she winds up falling in love with this fictional persona.
The distinctive quality of Achard's plays was their dreamlike mood of sentimental melancholy, underscored by the very titles which were primarily taken from popular bittersweet songs of the day. 1924's Marlbrough s'en va-t-en guerre (Marlborough Goes Off to War), 1935's Noix de coco (The Coconut), 1946's Auprès de ma blonde (Close to My Blonde) and Savez-vous planter les choux? (Do You Know How to Plant Cabbage?) and 1948's Nous irons à Valparaiso (We're Going to Valparaiso) are among some examples of this specific style.
Achard's greatest successes and popularity were in the period between the two World Wars when contemporary critics favorably compared him to some of his renowned French predecessors such as Pierre de Marivaux and Alfred de Musset. Postwar pundits were not as kind, pointing out the rather narrow scope of human psyche that he represented and deprecatingly referring to him as a "spécialiste de l'amour" ("love specialist") for the sickly-sweet characteristics of his poetic imagination.
The critics focused, of course, on Achard's most popular plays, disregarding the fact that the reason Achard continued to write them is precisely because they met with such unvarying success. His less-well known works, however, show innovative techniques and original themes. 1929's La Belle Marinière (The Beautiful Lady of the Canals a/k/a The Beautiful Bargewoman) still has some of the excessively-poetic dialogue, but is overall a realistic play about a love triangle involving a bargeman, his wife and his best friend and companion. Similarly, 1933's La femme en blanc (The Woman in White) uses a then-new technique of recreating for the audience events as they are being described by the play's characters. In 1938's Le corsaire (The Privateer) uses the "play-in-a-play" device pioneered by Luigi Pirandello, showing film actors portraying the life of a long-ago pirate finding themselves caught in an endless loop of similarities. The same year saw his most controversial play Adam, which portrayed the life of a homosexual. At the time, it created a scandal, but three decades later, in the radicalized culture of the late 1960s, it had come to be judged as tame and below Achard's usual literary standard.
After World War II, despite the criticism, Achard's literary output continued unabated. Among his most successful later plays were 1952's Les compagnons de la Marjolaine (The Companions of Marjoram) and 1955's Le mal d'amour (Love Sickness). The greatest popularity, however, was achieved by a 1957 comedy about a testy, ill-tempered character nicknamed Patate (Spud) and a 1962 comic mystery L'idiote (The Idiot), best known in America as the basic for the play and film A Shot in the Dark.
Four of Achard's plays also had Broadway runs. Domino, adapted by actress-writer Grace George opened at the Playhouse Theatre on August 16, 1932 and closed after seven performances. The title role was portrayed by silent-screen star Rod La Rocque. A much better run was enjoyed by Auprès de ma blonde, which was reworked by famed scenarist S. N. Behrman into I Know My Love. It opened at the Shubert Theatre on November 2, 1949 and ran for 247 performances, closing on June 3, 1950. The stars were Alfred Lunt and Lynn Fontanne. Patate, adapted by Irwin Shaw repeated the seven-performance fiasco of the previous one-name character, Domino. It opened at Henry Miller's Theatre on October 28, 1958 and closed on November 1. The fellow of the title was Tom Ewell. A Shot in the Dark would boast the longest run. Adapted by Harry Kurnitz and directed by Harold Clurman, it racked up an impressive 389 performances, opening at the Booth Theatre on October 18, 1961 and closing on September 22, 1962. The stars were Julie Harris, Walter Matthau and William Shatner.
Achard's numerous screenplays, frequently centering on relatively recent historical events and personalities, include 1936's Mayerling, 1938's Orage and 1942's Félicie Nanteuil. He was elected to the Académie Française in 1959.
Marcel Achard died in Paris at the age of 75.