M. Shadows was born Matthew Charles Sanders on July 31, 1981 in Huntington Beach, California. He began singing at an early age, but his interest in rock and heavy metal music grew as he became older and began to play the guitar. He links his early musical experience with the piano as a major factor in developing his skills with the guitar and his voice. He attended Huntington Beach High School, where he played for a brief stint in a punk band named "Successful Failure". Following this, Shadows formed Avenged Sevenfold in 1999 along with middle school friends Zacky Vengeance, The Rev, and Matt Wendt.

Rumors were spread that Shadows had lost his ability to scream due to throat surgery needed after Warped Tour 2003. However, Producer Andrew Murdock put down these rumors by saying: "When I met the band after Sounding the Seventh Trumpet… Matt handed me the CD, and he said to me, 'This record's screaming. The record we want to make is going to be half-screaming and half-singing. I don't want to scream anymore… the record after that is going to be all singing.'"

Shadows was specifically looking to add a more gritty, raspy tone to his voice and worked with Anderson for several months on this before City of Evil was recorded. This change resulted in newly established vocal contributions from each band member during live performances, and remained prevalent on every record the band has released since 2005.

Shadows has made guest appearances on numerous albums by various artists. He is featured on the Steel Panther album Feel the Steel and sings a verse of "Turn out the Lights." He also produced The Confession's 2007 album, Requiem, which, according to an interview, M. Shadows was one of the first steps which led to Avenged Sevenfold self-producing their 2007 self-titled album. Shadows also sings In "The River" by Good Charlotte on the album Good Morning Revival along with fellow band member Synyster Gates with his guitar solo. In 2012 Shadows and fellow Avenged Sevenfold member Synyster Gates made a brief cameo in the war game Call of Duty: Black Ops II in which they provided the voiceover of. Also, in June 2013, Matt competed in the sold out 128-team Call of Duty bracket at MLG Anaheim, placing in the Top 48. The April 2013 release of the band Device's self-titled album featured his vocals throughout track 9, "Haze". Shadows also sang "Nothing to Say" in Slash's self-titled solo album, as well as "Go Alone" in Hell or Highwater's debut album. He was also featured on Fozzy’s album Sin and Bones singing alongside Chris Jericho in the song “Sandpaper”.

Shadows married Valarie DiBennedetto on October 17, 2009. The couple have two sons, born in 2012 and 2014. M Shadows' sister is Amy Sanders, who is two years younger than he is. His fellow band member, Synyster Gates, is married to his wife's sister Michelle DiBendetto, making Shadows and Gates brothers-in-law.

Shadows draws his singing and performing style heavily from classic metal bands. He cites Guns N' Roses as his biggest influence, commenting, "I love that band. You can compare us all you want—they're a huge reason why I'm even in a band and even write music." Shadows also commented that he was heavily influenced by Metallica, Megadeth, Pantera, Slayer, Iron Maiden, Ozzy Osbourne, Black Sabbath, Led Zeppelin, AC/DC, Blind Guardian, Dream Theater, Slipknot, Beastie Boys, and Guitarist Scott Taylor. "Megadeth are the reason why Avenged Sevenfold try to infuse a classic metal sound into their music. " said Shadows in an interview, "It's 'cause we have that traditional classic sound that bands like Metallica and Megadeth paved the way for a while ago. That sound crosses over and the extreme metal doesn't," he added.

As of March 21, 2018, Shadows was named the 2018 official golf analyst of The Dan Lebatard Show With Stugotz on ESPN Radio and the leader of the Gotz Army.