Marty borrows his looks mostly from his father. With the exception of his curly hair, Marty's figure and face are nearly identical to Jay's. His most common outfit is that of a red, long-sleeved sweater over an off-white dress shirt, tan pants, and loafers.
Marty is shown to be overall kind and polite, even to the point of being seen as naive. However, there are often times were he will feel insecure about his appearance and abilities.
Jay and Ardeth have split custody over Marty since they are divorced; he lives mainly with Ardeth but has frequent visits with Jay. Him and Jay seem to have a good relationship, although in A Day at the Races and a Night at the Opera, he admits to a phycologist that he feels that Jay pretends that there's nothing wrong with Marty at all rather than addressing his son's problems.
While Marty and his father seem to get along fine, he seems to favors Ardeth more due to having more privileges in her vicinity. Sometimes he can be seen doing some outrageous activity with "Uncle Al," Ardeth's supposed boyfriend.
Carmen is a Cuban girl that Marty he met at school on Career Day. After following his father's advice, Marty goes on an (unsuccessful) date with her and then follows her back to Cuba. They confessed their feelings for one another by the end of their second date; however, due to her responsibilities in her own country she stayed in Cuba, never to be seen by Marty again.
Marty appears in every episode with the exceptions of:
- Dial 'M' For Mother
- Every Doris Has Her Day
- Sherman, Woman and Child
- Siskel & Ebert & Jay & Alice
- A Song for Margo
- Frankie and Ellie Get Lost