Upon arriving in Rio, Margret became reacquainted with H. A. Rey and persuaded him to leave his brother-in-law's firm. Together, they founded the first advertising agency in Rio de Janeiro and were married on August 16, 1935.

They created stories for newspapers and magazines, with Margret's writing and H. A.'s illustrations. Margret also continued her photography, and H. A. found steady work with Hoffmann-LaRoche, a pharmaceutical firm. He produced many of their direct mail advertising campaigns, utilizing witty illustrations. He also drew maps and posters, illustrated cookbooks and designed Christmas cards for corporate clients.