Reggae music originated in Jamaica in the 1960s and can be quickly identified by its characteristic "off beat" rhythmic structure. Reggae music can be associated with ska or rocksteady, two other Jamaican music styles, though reggae's tempo moves slower than ska and slightly faster than rocksteady. Writing a reggae song doesn't require a Jamaican background. If you understand the rhythmic structure and the lyrical content, you can write a reggae song that will bring home the spirit of Jamaica.
Develop a strong lyric first. Your lyrics can be about anything you want them to be, but many reggae songs focus on lyrics that are heavy with social criticism. Religion and political awareness are also good subjects for reggae songs. "I Shot the Sheriff" sung by Eric Clapton is an example of strong reggae lyrics. The song was written by Bob Marley and was originally reggae. Write your lyrics in a verse, verse, chorus, verse, chorus format, with the ending chorus repeating until fade out. The verses should tell the story of the song and each should be different, where the chorus is usually the same words and the part of a song typically sung several times.
Write in a simple 4/4 time. Three or four chords will do. The chords can be major, minor, or any combination. Add seventh chords for a more complex sound, but the main focus of the reggae song will be the way the chords are played, typically by putting emphasis on the second and fourth beats of each bar of music. These accented beats should be written as short musical "stabs." A good way to write the chord pattern is by alternating quarter and eighth notes with the eighth notes cut short. This creates the characteristic backbeat associated with reggae.
Write a bass line that repeats itself throughout the song. Consider writing the bass line so it accents alternating beats with the rhythm guitar. Don't write a lot of movement in your reggae song. The solid groove (the offbeat rhythm) is the feel you want to carry your song through to the end.
Keep the vocal melody simple. The rhythm of the music and the content of the lyrics is more important than singing technique. Write with a melody that people can sing along with. A simple melody will not contain many high notes or screaming. Avoid complex groups of notes sung together or big vocal jumps from low to high or vice versa. Reggae is participation music. The classic "I Shot the Sheriff" exemplifies a simple melody containing word repetitions characteristic of a reggae vocal. The song should engage and inspire listeners to sing along, and the notes you choose for the vocal melody should make it easy for them to do so.