Ronnie Winslow
Ronnie is the eponymous Winslow Boy in the title; a mere fourteen years old, he is thrown into an extremely complex and adult situation when he is charged with stealing a five shilling postal order whilst a cadet at the Royal Naval College. He is really steamrollered during the case; his family are not told of the accusations or the investigation and he has no legal representation. Fortunately he has a family who love and believe in him and when they do find out about his predicament leap into action in his defense. This speaks highly of his character, in that he has been an honest kid prior to this alleged incident, and they do not question his innocence.
Ronnie is somewhat of a paradox as a protagonist because he is the character whom the entire play revolves around, but is nonetheless one of the less developed characters as well. Ronnie is a sympathetic character for a number of reasons; he is innocent yet being treated as though he was guilty. He is just a kid, but being treated as if he is an adult murder suspect rather than a juvenile petty thief. He is also an underdog, which inherently makes us root for him. Ultimately he is exonerated of all charges and is able to go on with his military career.
Arthur Winslow
Arthur Winslow is Ronnie's father and he does not doubt his son's innocence for one moment. He is highly protective of him, and is also extremely pro-active in his defense of his son. He knows that he is going up against the entire machinery of the British military but is not scared because he knows that he has right on his side. He puts together a good team for his son, hiring the top attorney available, and making sure to support his daughter in her defense of her brother. It is also interesting to note that he has raised a daughter who is a suffragette, and is supportive of her, showing that he is open minded and fair when it comes to equality, and equal opportunity. This is also shown by his defense of his son who is not being treated fairly.
Catherine Winslow
Catherine is Ronnie's sister and is very protective of him. She is a combative woman who is a suffragette, and participates in many protests trying to fight for the right to vote for women. She does not doubt her brother and is keen to get involved with his case. She even does a little investigation of her own. Catherine's life is affected very detrimentally because of the entire debacle surrounding her brother's case. Her fiance ends their relationship because of pressure from his father, who is a military man through and through and automatically believes the military to be in the right come what may. She is aware that she needs to marry and resigns herself to marriage to Desmond Curry, her family attorney; she doesn't love him but she knows he is fond of her, and knows he will be a good husband. She ultimately ends up in a budding relationship with barrister Sir Robert Morton, whom she initially doesn't like and doesn't trust, but ultimately comes to respect, and finds that an attraction blooms between them.
Sir Robert Morton
Sir Robert is hired by Ronnie's family to defend him in court. He is respected and feared by opposing barristers and the prosecution in particular, because he is shrewd, fair and somewhat of a barracuda in the courtroom. He does not take the case for political reasons, but because of his belief in Ronnie's innocence after spending some time questioning him and really taking the trouble to listen to his answers. He initially alienates Catherine because he does not think that women should be allowed to vote. He wins her over, though, by turning down the position of Lord Chief Justice which is offered to him contingent on his dropping the Winslow case, which he refuses to do.
Desmond Curry
Curry is a good attorney and is the Winslow's family lawyer, although he is not a barrister and therefore not able to actually defend Ronnie in court. He is diligent and hard-working and does not mind working as a junior member of the defense team with Sir Robert Morton. He is good at investigating and is definitely instrumental in getting Ronnie's case heard in the first place. He is very fond of Catherine and would like to marry her but his romantic feelings remain un-reciprocated.