Although The Simpsons has a floating timeline in which the characters do not age, and the show is set in the current year, certain dates have been given. According to one source, Homer Simpson was born c. May 12, 1955 in Winnipeg, Manitoba, which makes him a Taurus, and was raised on a farm with his parents, Mona and Abraham Simpson. In the mid-1960s, while Homer was between nine and twelve years of age, Mona went into hiding following a run-in with the law. Homer attended Springfield High School and fell in love with Marge Bouvier in 1974. Marge became pregnant with Bart in 1980, while Homer was working at a miniature golf course, turning the crank that spins the windmill (sometimes too quickly).
The two were wed in a small wedding chapel across the state line, spent their wedding reception alone at a truck stop, and the rest of their wedding night at Marge's parents' house. After failing to get a job at the Springfield Nuclear Power Plant, Homer left Marge to find a job by which he could support his family. He briefly worked at a taco restaurant called the Gulp n' Blow, until Marge found him, and convinced him to return. As a result, Homer confronted Mr. Burns and secured a job at the Plant. Homer's salary is only $6,000 a year. Marge became pregnant with Lisa in 1983, shortly before the new couple bought their new house.
In 1985 and 1986, Homer saw brief success as the lead singer and songwriter for the barbershop quartet the Be Sharps, even winning a Grammy. During his time with the group, Homer was frequently absent from home, which put stress on his marriage. After the group broke up due to creative differences, Homer went back to Springfield to continue his old life. Some time in the late 1980s, Homer and Marge carefully budgeted so Homer could work at his dream job, pin monkey in a bowling alley. Unfortunately for Homer, Marge became pregnant shortly after he started his new job, and not being able to support his family, he went back to the Nuclear Plant.

According to comments made on The Simpsons DVDs by the writers and producers, Homer's age was initially 34, but as the writers aged, they found that he seemed a bit older too, so they changed his age to 38. Some episodes have different ages. In "The Homer They Fall", he is 38 years old; in "The Wizard of Evergreen Terrace", he is 39; and in "Springfield Up", he is 40.

Homer's baldness is often the subject of small jokes. Homer will sometimes lose the two strands of hair from the top of his head and exclaim "I'm bald!". Homer's baldness is not normal male pattern baldness, but is due to his children. Every time Marge informed him she was pregnant, he screamed, tore out some more hair, and ran upstairs to his room.