- “Extremely stubborn and suspicious.”
- ―Michael's description on Mary Poppins' tape measure
Like Jane, Michael had possessed a naughty streak which caused the resignation of 6 nannies in four months. However, upon Mary Poppins' arrival, it appears that he isn't as bad as is said. Her tape measure describes him as extremely stubborn and suspicious. He also seems to be friendly and playful.
At the beginning of the film, he is distant from both his parents. He seems to feel insecure due to failing to live up to George's ridiculously high standards for him, Winifred and Jane, and mistakenly believes that George hates him, though this changes by the end.
Michael's first appearance is when he and Jane are brought home by Constable Jones. They had been separated from their nanny, Katie Nanna, after having trouble with their kite. She insists it was intentional and resigns as a result, but from their perspective, it was merely an accident.
Later, when George and Winifred are drafting an advertisement for a new nanny, Jane and Michael bring their own. Theirs suggests that they have played several pranks on their former ones, but also calls for a fun one who will love and play with them. The more practical George dismisses the ad as ridiculous, tears it up, and tosses the pieces into the fire.
The next morning, Michael is seen watching the nanny applicants, all stern old women, who have responded to George's ad for a tough, commanding one. Much to his surprise, a sudden wind blows them all away. Jane and Michael notice a woman that fits their ad, flying by using an umbrella. Michael initially believes her to be a witch, but he is corrected by Jane, who says that witches have brooms.
Later, the woman comes to the nursery and introduces herself as their new nanny. After being amazed by her bottomless carpet bag, (though Michael crawls under the table to examine it), she measures both of them with her tape measure. It says that Michael is "extremely stubborn and suspicious." After he requests that she be measured, he learns that her name is Mary Poppins. She then leads them in a game called Tidy Up the Nursery. Both Jane and Mary are able to snap their fingers, causing the toys to put away by themselves. Michael, however, can't snap his, and when he finally does, he ends up in the closet, unable to get out because the doors keep opening and closing by themselves. He enjoys the "game" anyway.
Then Mary takes the children on an outing in the park. They intend to go there, but run into Bert, an old friend of hers. He tells the children about her magic and is able to convince her to transport them into his picture of the English countryside. While he and Mary enjoy a walk through the countryside, Jane and Michael enjoy a nearby fair. They meet up at Mary's private carousel, where she causes the horses to jump off. In a bit of competitiveness, Michael makes his go faster than the rest, before being restrained by Mary. Eventually, they end up at a race course, where Michael witnesses Mary effortlessly win the race. He learns of her magic word, Supercalifragilisticexpialidocious, but they are soon forced to leave when a rainstorm hits, which washes the drawing off. That night, Mary puts the children to bed and denies that anything unusual happened.
The next day, Mary, Jane, and Michael are out to do errands, but are called to the assistance of Mary's Uncle Albert by a dog named Andrew (she is able to understand him, though Michael believes he said nothing). They go to the house to find Bert already there. The children discover that Uncle Albert "suffers" from a condition where he uncontrollably floats to the ceiling when he laughs. Despite being warned by Mary, the condition spreads to Bert and the children. At Uncle Albert's request, they stay for tea after Mary makes the table float into the air. Eventually, everyone comes down at the sadness of being told they must leave.
That night, George attempts to fire Mary after hearing the children's unbelievable tales. However, they are happy to find that she has not been fired. Michael is puzzled, however, when she announces they will go on an outing to the bank with George, as he had never taken them anywhere. Mary tells them about the Bird Woman, who allows people to feed the birds for tuppence nearby.
Michael goes with George and Jane to the bank and secretly brings tuppence to feed the birds. George refuses to let him, however, and attempts to convince him to invest it in the bank. He is almost convinced but is angered when the owner, Mr. Dawes Sr., takes it without asking. His attempt to retrieve it begins a run on the bank.
In the chaos, Jane and Michael escape from the bank. They become lost but soon run into Bert, who is working as a chimney sweep. They reveal the trouble at the bank but do not seem to understand what went wrong, though they believe that George hates them for it. He helps them to understand that George does not hate them, but is merely trapped in a cage by his responsibilities. He takes them home and is unwittingly enlisted to watch them by Winifred, as it is Mary's day off. He allows them to help him clean the chimney. As they are working, Mary returns and warns them of the danger, just as Michael is sucked up it. Jane, Mary, and Bert follow, and Mary leads them on an expedition of the rooftops. They run into Bert's chimney sweep friends, and party all the way back to the Banks' living room. Bert runs out the chimney sweeps when George returns home, who catches Michael trying to leave with them.
After hearing that George is in trouble for the events at the bank, Michael gives the tuppence to him, in the belief that it will help fix things. The next morning, Mary is preparing to leave, much to Jane and Michael's disappointment. However, they soon hear George calling them, though he doesn't believe it to be him, as the voice is happy. They head downstairs and discover that he has fixed their broken kite. During the night, he had a change of character and had decided to become a more involved father. He takes his family kite flying. Michael is so happy to be with him, that he forgets to say goodbye to Mary, though she notes that that is as it should be. He is last seen happily flying his kite alongside his family.
In 1935, Michael is now much older. He now works at the bank that George worked at, and the film takes place during the time of the Great Slump. He has married his longtime girlfriend, Kate, and by her, he has three children. Unfortunately, he is very strict and harsh with them in as much the same way that George was to him and Jane when they were kids, likely as a result of depression over Kate's death.
In the opening, there is a chaotic scene where the kids, who have been taught by Michael to take care of themselves, hear reports from some lawyers from the bank, that their house is going to be repossessed to repay a large loan that Michael took from the bank to cover his losses during the Great Slump. The bank is now run by Mr. Dawes, Jr.'s nephew, William Weatherall Wilkins who is a corrupt businessman using advantage of the Slump to repossess houses for no reason, though Michael is unaware of his plot. By this point in their lives, Michael and Jane have also stopped believing in Mary Poppins' magic, dismissing it as their imaginations.
The only way to avoid having their house repossessed is to repay their loans by Friday at midnight and the way to do that is to locate the shares in the bank that their father left them. Michael and Jane search the attic and the downstairs' office for the shares, but they come up fruitless. At the same time, Mary Poppins returns to the household to restore order for the Banks family, and, just as in the original film, hires herself as the kids' nanny despite the father's (in this case, Michael) skepticism.
Michael and Jane try to find records of their father's shares at the bank with Mr. Wilkins at the bank, but he pretends to not have any on file and, as soon as their backs are turned, he throws the records in the fire to destroy any evidence of it.
One day, Michael's children embarrass him during a visit to the bank (set up by Mary Poppins) and Michael snaps at them at the house, telling them that the rumors about the bank repossessing the house, are true, and that they could have lost him his job. Michael then mentions their mother and asks if they haven't lost enough already. Now nearing tears, the children cheer up their father by singing a song sung to them by Mary Poppins, and he feels better, telling his children that even if the bank repossesses their house, they still have each other.
The next day, the family packs up to evacuate the house, knowing they have lost. But, when one of Michael's children brings the repaired kite from Michael & Jane's first time with Mary, Michael realizes that the kids repaired the kite using a drawing on the back of the shares' certificate. Realizing that they now have proof, Michael and Jane rush to the bank in order to save their house. With help from Mary Poppins and her new partner Jack, the kids and Mary go to "turn back time" - climbing Big Ben in order to alter the clock so that it doesn't strike midnight before Jane and Michael can prove their shares.
Jane and Michael try to enter the bank, but Mr. Wilkins has his henchmen - the attorneys, lock the door. So they use the kite to bring the certificate to Mr. Wilkins' office and, after one of the attorneys, who sympathizes with the Banks family, changes sides and allows them inside the bank, they go up to Mr. Wilkins' office. Unfortunately, they are missing the piece of the certificate with their father's signatures on it, and Wilkins seemingly has won. An angered Michael Banks tells Wilkins he can have the house, that he should have listened to his children earlier, and that the family has all they need. However, lucky for the Bankses', Mr. Dawes Jr. comes into the room out of nowhere to save the day; he chastises his nephew for his corrupt practices, fires Mr. Wilkins from his position as president of the Fidelity Fiduciary Bank, and orders Hamilton and Frye to escort Wilkins away while allowing the Bankses to use their father's invested tuppence from the first film, and the return from the investment, to repay their loan in full, saving the house in the process.
The Bankses celebrate their victory by flying balloons at a Fun Fair, and Michael and Jane realize from their balloon flights that Mary Poppins' magic has always been real. Eventually it is time for Mary Poppins to leave and Michael and Jane look up in the sky, watching Mary fly off with her umbrella, and Michael thanks her for saving their house.