The Warrior's Code was the first Dropkick Murphys studio album to feature Tim Brennan and Scruffy Wallace.

"Your Spirit's Alive" was written in memory of the band's friend Greg "Chickenman" Riley, who died in a motorcycle accident in 2004.

"The Warrior's Code" is about Lowell, Massachusetts boxing legend Micky Ward, who is also shown on the album's cover.

"Sunshine Highway" was the first single from this album and has been featured on Royal Caribbean's Sports' Deck, even though the song is about drug rehabilitation.

The band also performed an acoustic version of the song "Fields of Athenry" at his funeral; the recording was included as the B-side for the single.

Allmusic gave the album a rating of 3.5 out of five stars, praising the "alternating lead vocals, a tag team of rage and bravado.

Punknews.org had similar praise for the album, stating: "This is a dynamic record that frequently changes gears between faster punk and hardcore tracks and more subtle renditions of traditional material.