A demo of the song "The Deceived" was included on the re-release of Trivium's debut album Ember to Inferno nearly a year before Ascendancy was released. Likewise, a demo version of "Like Light to the Flies" was included on the MTVcompilation albumHeadbangers Ball Volume 2. Also, a demo of the song "Blinding Tears Will Break the Skies" was included on the Ember to Inferno re-release and later re-recorded and included as a bonus track on the re-release of Ascendancy.
Speaking to Kerrang! about the songs lyrics, Matt Heafy said: "Definitely, some of the lyrics are about my personal insecurities and my social issues and disorders, and there's a thing about quietness in the music industry – people assume you're a dickhead if you don't want to talk, and that was definitely said about me. Being in a band forced me to have to get over my awkwardness around people and you can really see what I was going through in there."
Since its release, Ascendancy has sold over 500,000 copies worldwide. In the U.S., the album peaked at No. 151 on the Billboard 200 and at No. 4 on the Top Heatseekers charts, selling over 140,000 units. In the UK, it peaked at No. 78, and shipped over 100,000 copies, attaining Gold status, without entering the UK top 75.
Upon its release, the album received critical acclaim. In a very positive review, Johnny Loftus of Allmusic had this to say about the album, "Ascendancy aligns real-deal thrash with powerful modern influences. But at all times it's a platform for Trivium's own crazed talent."