Ward's drug and alcohol use increased throughout Black Sabbath's heyday. By the late 1970s he was drinking during gigs, something he had never done before. He also began experiencing panic attacks. Ward has said he cannot remember the recording of the 1980 album Heaven and Hell due to his alcohol abuse. According to Black Sabbath bandmate Iommi, Ward disappeared on 21 August 1980, without saying goodbye, other than a telephone call to then-Black Sabbath vocalist Ronnie James Dio informing him "I'm off then, Ron." He then briefly played in a band called Max Havoc. He sat out one album (1981's Mob Rules) before returning to Black Sabbath for 1983's Born Again album. Ward once again left for health reasons before the band toured in support of Born Again. He again rejoined Black Sabbath in 1984 to record new material with David Donato but after several demo tapes, he once again left Sabbath.
According to Tony Iommi, he and the band would often set Ward's beard on fire and perform other harmful pranks on him. On one occasion, Ward even received third-degree burns. In an interview with Guitar World, Tony described it as follows:
Bill and I were in the studio rehearsing one day and out of the blue I asked him, "May I set you on fire, Bill?" And he said, "Well, not now, not now." And then I forgot about it. Later on when the day ended, he said to me, "Well, I'm going home now; you still want to set me on fire or what?" And I said, "Sure." So I took a small can of lighter fluid and sprayed it on him, lit a match, and whoomph. He was wearing these polyester pants so they burned really quickly and he was on the floor screaming and crying. I could not help him because I was so busy laughing. It actually turned out to be quite serious. I felt really bad for him. He was sent to the hospital. Later on, his mother called me on the phone and said, "You barmy bastard, it's about time you grew up. Our Bill is going to have his leg off." But things like that always happened to Bill.
Iommi claims that Ward almost died after a prank-gone-wrong during recording of Black Sabbath Vol. 4 in 1972. The band were renting a Bel Air mansion belonging to John DuPont of the DuPont chemical company. The band found several spray cans of gold DuPont paint in a room of the house; finding Ward naked and unconscious after a night of heavy drinking, they thought it would be funny to cover the drummer from head to toe in gold paint. Ward soon became violently ill and had a seizure and an ambulance had to be called. The paint had blocked all of Ward's pores, which his bandmates were subsequently informed can be fatal.
During the recording of Heaven and Hell in 1980, Iommi doused Ward with a solution used by studio technicians to clean the tape heads. He then set light to the solution, which was much more flammable than Iommi had anticipated. Ward suffered third degree burns as a result and still has scars on his legs from the incident.
After a few years in hiatus, Ward decided to return to playing music in the late 1980s. In 1989 he went to work on a solo album, which featured a huge array of guest musicians, including former Black Sabbath bandmate Ozzy Osbourne and his guitarist, Zakk Wylde. Released in January 1990, Ward One: Along the Way showcased Ward's versatility in musical tastes and abilities; he even sang vocals on some of the songs. It would be seven years before he released his second solo album, When the Bough Breaks, in 1997.
In 2002 he released the song "Straws" as a single for charity. The song would reappear on his 2015 album Accountable Beasts.
Before the full Black Sabbath reunion, Ward and the original Sabbath had reunited twice for short sets, first for Live Aid in 1985 and then at a Costa Mesa, California Ozzy Osbourne show on 15 November 1992. Sabbath, with Judas Priest singer Rob Halford replacing Ronnie James Dio who had recently left the band, opened the show for Osbourne. The Ozzy Osbourne band (Osbourne, Zakk Wylde, Mike Inez, Randy Castillo and John Sinclair) then did a full set before Osbourne was reunited with Iommi, Butler and Ward for four numbers.
Ward made a brief return to the band for a South American tour in 1994 with Tony Martin fronting, before finally rejoining the band for the two shows at the Birmingham NEC, England on 4 and 5 December 1997, which made up the Reunion album. When what was billed as the original line-up reunited for the Ozzfest tour in 1997, Mike Bordin played drums.
Ward was forced to skip all but the last two Black Sabbath appearances in 1998 while he recovered from a heart attack suffered during the tour rehearsals that May. As the band rehearsed, Ward stopped and asked if he could lie down for a spell. He then asked for his assistant and informed the band that his arm had gone numb. Iommi and Butler then left for a short time, not knowing the severity of Ward's condition. Outside, they saw an ambulance pass but weren't aware what was happening. Upon returning to the rehearsal space a short time later, a frantic Osbourne informed them "Bill has had a heart attack! Bill has had a heart attack!" As was the case in 1980, he was replaced at short notice by Vinny Appice, although this time it was always intended to be a temporary absence for Ward, health permitting.
In 2000, Ward participated in a partial Black Sabbath reunion of sorts, joining Iommi and Osbourne to record the track "Who's Fooling Who" for Iommi's first solo album.
Since mid-2002, Ward has done a monthly internet-only radio show named Rock 50 on radio station WPMD from Cerritos College in California. Ward plays a variety of metal, hard rock, and some classic rock.
Brief reunion with Black Sabbath
In October 2006, news leaked that Ward would be reuniting with Tony Iommi, Geezer Butler and Ronnie James Dio for a tour though under the moniker Heaven & Hell. However, Ward later decided not to participate in the tour or continue participation in the band because of musical differences with "a couple of the other bandmembers" and a reported concern about extended touring.
On 11 November 2011, Iommi, Butler, Osbourne, and Ward announced that they were reuniting to record a new album with producer Rick Rubin and to start touring in 2012. In February 2012, however, Ward left before work commenced on 13, the first studio recording to include original band members Iommi, Osbourne and Butler since the live album Reunion (1998), which contained two new studio tracks. Ward said that he had failed to reach an agreement regarding his contract. However, he did later admit that his weight would have been an issue in a 2013 tour. Osbourne also suggested in an open letter that Ward's decision not to take part was down to his health. In April 2015, Ward criticised Osbourne on his Facebook fan page via a letter to his and the band's fans. Which prompted a rebuttal from Osbourne on his Facebook page:
Bill, stop this smokescreen about an "unsignable contract" and let's be honest. Deep down inside you knew you weren't capable of doing the album and a 16 month tour. Unfortunately for you, our instincts were correct as you were in hospital several times during 2013. Your last hospitalization was for a shoulder surgery that you now say you've only just recovered from. This would have meant that our world tour would have been canceled. So how is all of this my fault? Stop playing the victim and be honest with yourself and our fans.
Ward's surgery on his shoulder prevented him from playing drums again until May 2014, delaying his third studio album Accountable Beasts. He had also expressed a desire to tour behind the album once it is released, provided that sales were acceptable.
Ward says he has "lost a friend" in Osbourne, but maintains contact with Butler and Iommi; if they could "come to some terms", if Ozzy would make amends for statements he made in 2012 and 2013, he would rejoin Black Sabbath.
Ward reunited with Sabbath members Tony Iommi and Geezer Butler to accept the "Lifetime Achievement" award at the May 2015 Ivor Novello Awards.
In 2016, Ward debuted with a new band called "Day of Errors", which played its first gig in June that year at Gaslamp in Long Beach, California and also features Joe Amodea on guitar/vocals and Kill Devil Hill singer Jason “Dewey” Bragg on vocals.
Ward was due to play a string of dates with his new band in December 2017 but had to cancel these when he was hospitalised with heart problems in November.
He once again reunited with Iommi and Butler in Los Angeles in May 2019, as Black Sabbath were awarded a Lifetime Achievement Grammy. Though Sabbath did not perform, Rival Sons performed a set of their songs for the occasion.  A short time later Osbourne said in an interview that he wants to play one last show with the band's original lineup. Ward announced 3 weeks later on his instagram that he loved all 3 of his former Black Sabbath bandmates very much and was open-minded to playing a very last show with them.