The album was partially recorded with original guitarist Pete Willis, whose rhythm guitar tracks appear on all songs. Midway through the recording sessions, Willis was fired for excessive alcohol abuse and was replaced by guitarist Phil Collen, who contributed a few guitar solos that had not yet been recorded by Willis. On the original LP release, Willis is visible in the background of the photograph of lead singer Joe Elliott, while Collen is given his own personal photo as the new full-time member of the group.
Pyromania has received mostly positive reviews, being commonly considered, along with its follow-up Hysteria, one of the band's finest efforts to date and one of "Mutt" Lange's best productions. David Fricke of Rolling Stone magazine praised Def Leppard for putting "some much-needed fire back on the radio", producing sophisticated music "more emotionally charged than most of the synthesized disco that passes for 'modern music'" over the airwaves; he added that the band "may not be highly original, but they mean what they play" and "Lange's artfully busy mix" easily covers up any fault.AllMusic reviewer Steve Huey stated that Pyromania was "where the band's vision coalesced and gelled into something more." He also described the songs as "driven by catchy, shiny melodic hooks instead of heavy guitar riffs, although the latter do pop up once in a while", and added that "transcendent hard rock perfection on Pyromania was surprisingly successful; their reach never exceeded their grasp, which makes the album an enduring (and massively influential) classic."Sputnikmusic staff reviewer is equally enthusiastic and thoroughly recommends the album "filled with tight musicianship, infectious melodies and anthemic choruses" "to pretty much anyone… No matter what their taste in music is." On the contrary, Canadian journalist Martin Popoff considers Pyromania the beginning of Def Leppard's "creative degeneration" and criticizes Lange's "painstaking approach to detail" which strips the album "of its sweat and grit" to the level of making it sound "phony".
With its melodic hooks and heavy MTV exposure, Pyromania became a massive success, and was a major catalyst for the 1980s melodic hard rock movement. The album sold six million copies in the US in its original release (about 100,000 copies were sold per week for much of the year). It has since sold over ten million copies there and was certified diamond. In 1989, it was re-released by audio fidelity company Mobile Fidelity Sound Labs as part of their Ultradisc series. Three songs, "Photograph", "Rock of Ages" and "Foolin'", became top 40 singles on the Billboard Hot 100 in the US with the first two reaching the top 20. "Photograph" (6 weeks) and "Rock of Ages" (1 week) both topped the Billboard Top Rock Tracks while "Foolin'" and "Too Late for Love" made the Top 10. Three additional songs, "Comin' Under Fire", "Billy's Got a Gun" and "Action! Not Words" made the top 40 of the Top Rock Tracks chart.
In Canada, "Rock of Ages" charted highest on the Singles Chart at No. 24, while "Photograph" and "Foolin'" reached nos. 32 and 39, respectively. The hard rock nature of the songs resulted in some Top 40 radio stations choosing to play only one or two of the three singles, rather than all three. At CHUM-AM in Toronto, one of the largest audience Top 40 stations in Canada at the time, "Rock of Ages" never reached its Top 30 countdown whereas down the highway in Hamilton at the CKOC-AM Top 40 radio station it peaked at no.2. It also topped the chart at many album-oriented rock stations such as Q107 in Toronto.