When she was four years old Joan had an 18 year old live-in governess, Marie Sandow. In 1922, when she was six years old, she was selected for the leading role in a series of children's fairy story films: an article about this in the San Francisco Chronicle commented "Joan Woodbury has been known for some time as America's 100 Per Cent Child, and has been photographed, sketched and painted by many artists." She first studied for seven years in a convent, later trained in dance, and eventually graduated from Hollywood High School. Woodbury began dancing for the Agua Caliente dance company, and at 19 decided to attempt a career in acting.

She moved to Hollywood and that same year received her first acting role in the 1934 film Eight Girls in a Boat, which was uncredited. Another uncredited role followed, with her first credited role being in the 1934 film One Exciting Adventure, which starred Binnie Barnes. Her first major role, billed as Nana Martinez, was in a Hopalong Cassidy movie The Eagle's Brood. Woodbury appeared in fifteen films from 1934 through 1935, of which ten were uncredited.

In 1936, her career began to become more successful, with appearances in eight films that year, of which five were uncredited. However, of the three roles that were credited, Woodbury made an impact, and caught the attention of studios. Her mixture of Danish, British and Native American heritage gave her an exotic appearance, and allowed her to be cast in many different ethnicities, from Hispanic to French and Asian. By 1937 her career had taken off, mostly in B-movies such as Living on Love and Bulldog Courage, but also with her receiving many credited roles.

In 1937, Woodbury starred in her first of several credited Charlie Chan films, titled Charlie Chan on Broadway. She also began appearing in numerous westerns, portraying the heroine opposite some of the 1930s biggest Cowboy actors, to include william Boyd of Hopalong Cassidy fame, Roy Rogers, and Johnny Mack Brown. Woodbury would appear in fifty films from 1937 to 1945, almost all of which were credited. Her most memorable of that period was her lead role in the serial Brenda Starr, Reporter, in 1945.

On December 17, 1938, Woodbury married actor and Producer Henry Wilcoxon, with whom she had three daughters: Wendy Joan Robert (born 1939), Heather Ann (born 1947, named after Heather Angel) and Cecilia Dawn "CiCi" (1950, named after Cecil B. DeMille). They divorced in 1969. After the marriage, according to film critic Don Daynard, she "continued her career but never graduated from the minors", featuring in such films as Barnyard Follies, In Old Cheyenne and Brenda Starr, Reporter.

In addition to managing their company, she continued to act on occasion, with her biggest role after 1946 being a minor credited part in the 1956 epic The Ten Commandments, starring Charlton Heston, Yul Brynner and Anne Baxter. Her last film appearance was a supporting role in the movie The Time Travelers (1964).

When Woodbury retired she had appeared in 81 films, though a newspaper article published in 1963 reported that she had appeared in more than 300 films. Woodbury eventually settled in Desert Hot Springs, California, where she was residing at the time of her death at the age of 73.