When the Banks' latest nanny quits after being exhausted by their two children, they are forced to look for a new nanny. Mr. Banks wants a strict, authoritarian governess, while the children write their own ad looking for a fun-loving nanny. Their father throws their ad into the fireplace, but the remains float up the chimney.

The next day, Mary Poppins (Julie Andrews) floats down on to their doorstep (along with her magical umbrella and bottomless bag) in response to the children's ad, despite their father's confusion as to how she came across it. Over time, she helps bring joy and happiness back into the family's life.