Wachter was born in Pottsville, Pennsylvania. As a child, he spent most of his time with his family in New Jersey and Boston. An active child, he participated in baseball and soccer, taking up swimming as well, he also went to United States Space Camp, along with Space Academy. His interest in music bloomed when he was around five years old, and between the ages of five and eight, he experimented with various instruments, focusing primarily on the piano and drums.
Wachter reached the peak of his musical interest around high school and spent most of his time playing in bands. He picked up the bass, he stated, because he "wanted to play in a band, and the band needed a bass player." He had no previous experience with the bass, the closest being experimenting with the guitar. He credited former Metallica bassist, the late Cliff Burton, as his inspiration for wanting to play the bass guitar.
Wachter was rumored to have worked in a slaughter house, but confessed in an interview that he and his bandmates made up the story to stir up an otherwise dull interview.
Wachter joined Jared Leto, Shannon Leto, and Solon Bixler, rounding out the Thirty Seconds to Mars line-up, in 2001. Bixler was replaced with Tomo Milicevic in 2003.
Wachter often stands in a "pigeon-toed" stance (both feet turned in toward each other) when he plays his bass, and stares down at his feet. He says doing this allows him to focus on what he's playing and keeps him from being distracted by fans.
In the early days of Thirty Seconds to Mars, Wachter complained of consistent headaches after performing, but no pain while he was on stage. After a visit to the hospital and a CT scan, it was discovered that he developed a concussion from frequent head-banging on stage. This prompted his mother to suggest he "wiggle his hips like Elvis", as mentioned in the fan yearbook. The head-banging has since stopped.
The first two dates of the 2006 "Forever Night, Never Day" headlining tour had to be postponed after Wachter hurt himself. The injury resulted from changing one of his car's headlights (or as Shannon Leto says "He was left alone with a pair of scissors." to which Wachter replied "A pair of scissors and a light bulb. I'll leave the rest to your imagination."), pushing the tour back an additional two weeks. The band issued press release to fans on March 2.
While on tour in El Paso, Texas, on March 2, 2007, Jared Leto announced to the arena that Wachter would be playing his last show with the band. He dedicated the final song of the show, "R-Evolve", to Wachter. The group, with the exception of him then signed autographs for the El Paso fans. He returned two weeks later to resume play with the band and finish out the summer festivals.
Following the departure of Ryan Sinn from the band Angels & Airwaves, on 23 April 2007, Wachter has joined the band in Sinn's place on their current tour. He was later confirmed as a band member, and worked with Angels & Airwaves on their second album, I-Empire. The band released their third studio album, titled Love, in February 2010, along with its follow up Love: Part Two in 2011. On June 24, 2014, Tom Delonge posted a photo of Matt stating his intention to leave the band to focus on his family life at home, stating "Matt still might join us later down the road somewhere and somehow."
On March 9, 2017, a video posted to Tom Delonge's Instagram account shows Matt Wachter playing bass, to which Delonge states he has "been looking for [Wachter]". This has led to speculation that this could possibly show that Matt is back in Angels & Airwaves
Wachter serves as an occasional guest host on Get the Fuck Up (GTFU) Radio. The radio show is hosted by two of his friends, Aaron Farley and Jeremy Weiss and is featured on Little Radio, out of Los Angeles. He was also in a band in Boston called Strangle me.
In the Summer of 2009, Wachter recorded bass on all tracks for the upcoming release by Street Drum Corps, due for release in Spring 2010.
Wachter is an avid Boston Red Sox fan. He is also an avid fan of video games, like video game systems, such as GameCube, PS2, Nintendo, Xbox, and PlayStation. Wachter is a big fan of body art and claims to have over 20 tattoos. Some of these include "Rock-n-Roll" in script on his stomach, two swallows on both pectorals, a winged bomb on his right arm, and a switch blade with Latin quotation on his right side. These specific tattoos were done by artist Josh Hoffman at Olde City Tattoo in Philadelphia, Pennsylvania. He also has Dia De Los Muertos, or Day of the Dead skulls tattooed on each foot, as well as numerous other inkings in various locations. Wachter has a deer head tattooed on his right leg as well. He had this done while he was on tour in Japan. On his right inner arm he has yellow jackets to remind him that he is allergic. Also, on his chest there is a locked heart filled with his wife's name Libby.
On May 14, 2009, Matt and Libby (nee' Lawson) welcomed their first child, Sailor Mae Wachter.