- “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 an adult. He works at the bank that George worked at, and the film takes place during the time of the Great Slump pre-WWII times. He has married his longtime girlfriend, Kate, and they have 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 taking advantage of the Great 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's 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 George left them, which have increasing value. Michael and Jane search the attic and the downstairs' office for the shares, but they come up fruitless. At the same time, Mary 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 George'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, the kids embarrass Michael during a visit to the bank (set up by Mary) and he 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. He then mentions Kate and asks if they haven't lost enough already. Now nearing tears, they cheer him up by singing a song sung to them by Mary, and he feels better, telling them that even if the bank repossesses their house, they still have each other.
The next day, the Banks family packs up to evacuate the house, knowing they have lost. But, when one of the kids brings the repaired kite from Michael and Jane's first time with Mary, Michael realizes that they repaired it 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 and her new partner, Jack, the kids go to "turn back time" - climbing Big Ben in order to alter it 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, Hamilton and Frye, lock the door. So they use the kite to bring the certificate to Mr. Wilkins' office and, after one of the henchmen, who sympathizes with the Banks family, changes sides and allows them inside, they go up to Mr. Wilkins' office. Unfortunately, they are missing the piece of the certificate with George's signatures on it, and Wilkins seemingly has won. An angered Michael tells him he can have the house, that he should have listened to the kids earlier, and that they have all they need. However, lucky for them, an elderly and frail Mr. Dawes Jr. comes into the room out of nowhere to save the day; having been tipped off by Mary of Mr. Wilkins' true intents, he chastises him for his corrupt practices, and fires him from his position as president of the Fidelity Fiduciary Bank, taking back his job.
Mr. Wilkins, before leaving, tells Mr. Dawes Jr., in defense of his practices, that he's made the bank more money than the Dawes ever did, but Mr. Dawes Jr. scoffs at his defense and then orders Hamilton and Frye to escort him away while allowing the Banks family to use George'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. He also allows them to keep their bank shares without having to spend them, thus guaranteeing the kids, their future as adults.
The Banks family celebrate their victory by flying balloons at a Fun Fair on a very sunny day, and Michael and Jane realize from their balloon flights that Mary's magic has always been real. Eventually, it is time for her to leave and Michael and Jane look up in the sky, watching her fly off with her umbrella, and Michael thanks her for saving their house.
- In the sequel, Michael does share similarities with the adult Christopher Robin in the live-action film of the same name, where both have lost their sense of fun and imagination that they had as a child, who reunites with someone from their childhood during a crisis they're going through, and to show them what it like to be a child again (Winnie the Pooh and Mary Poppins), and have a supervisor whose related to the ageing CEO of where they work and as well as the main antagonist of the film, (Giles Winslow Jr. and William Weatherall Wilkins)