2002: Popstars: The Rivals

Semple took part in the ITV television series Popstars: The Rivals, a British singing competition.

• Week 1, he sang "Reach Out I'll Be There" from The Four Tops. He was safe.
• Week 3, he sang "Over My Shoulder" from Mike + The Mechanics. He was safe.
• Week 5, he sang "Sorry Seems to Be the Hardest Word" from Elton John and Bernie Taupin. He was safe.
• Week 7, in the boys' final, he sang "You Are So Beautiful" from Joe Cocker.

Host Davina McCall announced the names of the five contestants who had qualified for the boy band. Semple was the first member to be announced followed by Matt Johnson. Third was Daniel Pearce and fourth Anton Gordon. The last available place went to Jamie Shaw whereas Chris Park was eliminated from the boys competition.

Semple and the four other contestant winners (Anton Gordon, Matthew Johnson, Daniel Pearce and Jamie Shaw) went on to form the group One True Voice.

The same show had also produced the girl group Girls Aloud also won the competition.

2002–2003: One True Voice

Semple became a band member of the boyband One True Voice created as a results of the competition. The line up of the band was decided by public vote, who voted for their favourite male hopefuls each week to form the boyband. The name of the band was later shortened to OTV.

One True Voice was made up of:

• Anton Gordon (from London, England)
• Matt Johnson (from Deeside, Wales)
• Daniel Pearce (from Kent, England)
• Keith Semple (from Larne, Northern Ireland)
• Jamie Shaw (from Cardiff, Wales)

Their debut single, a double A side hit single "Sacred Trust/After You're Gone"^[1] went head-to-head with Girls Aloud on 16 December 2002, for the Christmas number one spot. One True Voice lost out to the girls and had to settle for the UK Christmas No. 2 position. The group's manager, Pete Waterman, has speculated that the show was fixed against OTV, but has not said how.. In any case, the single "Sacred Trust/After You're Gone" reached gold record status.

One more Top 10 hit followed, in the form of "Shakespeare's (Way with) Words", which reached No. 10 in the UK, in June 2003. A few weeks later it was announced that Daniel Pearce, who as arranger and co-writer of some of their songs had quit the group to pursue a solo career. The next day the group disbanded.

The group appeared at number 32 in Chantelle's Top 50 Reality TV Stars, ahead of both Phixx and Clea who also appeared in Popstars: The Rivals.

2003–2008: Solo career

After the split, Semple continued his musical career reforming his pre-OTV band, the Keith Semple Band, then fronted the band Alibi.

2006–2012: 7th Heaven

In 2006, Semple moved to the United States and joined Chicago-based rock band 7th Heaven as their lead singer. This resulted in a critically acclaimed album USA-UK alluding to the co-operation of this UK act in an American band.

During Semple's membership, the band consisted of members:

• Keith Semple – guitars, vocals (lead singer), keyboard
• Richard Hofherr – guitars, vocals, keyboard
• Mike Mooshey – drums
• Mark Kennetz – bass, vocals
• Nick Cox – guitar, vocals
• Tamara Mooshey – vocals

With Semple the band released a number of studio and live albums: Medley CD (2007), U.S.A – U.K. (2008), Unplugged (2009), Pop Medley 2 (2009), Medley CD/DVD (2010), Jukebox (2010), Merry Christmas in Chicago (2010) and Pop Media (2011). He left the band in 2012.

In 2012, Semple left the band and was replaced by Anthony Fedorov, a contestant finalist on the fourth season of American Idol.

2010: American Idol

In January 2010, Semple successfully auditioned for the ninth season of American Idol. He was put in the intro to the Chicago episode of the American Idol.

Semple said Simon Cowell was reportedly "unhappy" he did not tell his band members 7th Heaven in advance about his audition. But Fox Chicago affiliate offered to film Semple telling his band 7th Heaven^[2] and allowed them to perform together on Fox, thus giving him a fresh chance.

At the actual Chicago auditions, he sang the Bryan Adams' song "Heaven". Simon Cowell said "I'm going to pass", but the three other judges Kara DioGuardi, Randy Jackson and guest judge Shania Twain approved him going to the next round on a golden ticket.^[3]

But after the broadcast, it was revealed there was an immigration snafu about Semple's residency status, and that he being in the United States on a work visa and not as a permanent resident would disqualify him from applying to American Idol that stipulates that non-Americans applying to the show should at least have a permanent residency status, not a temporary working visa permit. The American Idol producers pulled the plug on Semple continuing with the competition and disqualified him.^[4]

Another former One True Voice band member Daniel Pearce had attempted a comeback less than a year earlier in 2009 on the sixth season^[5] of the UK The X Factor. Pearce was picked for the Final 24 but failed to make it to the Final 12.

2013–present: SEMPLE and The Cyberiam

After announcing his resignation as the lead singer of 7th Heaven in October 2012, Semple introduced his new band, SEMPLE. With members Johnny Jannotti (formerly of Chasing the Day), Drew Jonhson (formerly of Ordinary Outcasts), Amy Jay (formerly of Cat Fight) and Charley Bredrup (Fletcher Rockwell and The JR Miller Project).

At the end of 2013, Amy announced she would be leaving the band to pursue her post grad education. One year later, the band, functioning as a four-piece, mutually parted ways with Charley Bredrup. Following interim guitarists Paulie Felice (of Lexington, KY) and Stevie Craig, the position was permanently filled by Valentine Bennett (of McHenry, IL).

SEMPLE focuses on the original music Keith Semple has been writing and recording for years, as well as new material the band is working on together.

In 2016, Semple founded the progressive rock band The Cyberiam with keyboardist, Frank Lucas, and Lateralus drummer Tommy Murray.^[6] Along with bassist Brian Kovacs, they have released two studio albums, one EP, and two live albums to date. The Cyberiam have played at several progressive rock festivals, Progtoberfest IV in 2018, ProgStock in 2019, Marillion Couch Convention in 2020, and ProgPower USA in 2022 receiving a host of accolades.^[6] Keith and Brian toured as The Cyberiam Duo opening for Riverside in 2022.^[7]

U.S. The Voice

In 2015, he auditioned for season 9 of the American series The Voice. In the debut episode of the season broadcast on 21 September 2015, he sang "I'll Be There For You" with two of the four judges, Adam Levine and Gwen Stefani turning their chairs. Semple chose to be part of Team Adam.

Semple was paired against Manny Cabo in the Battle Rounds. They both sang The Who's "Baba O'Riley". Semple was declared the winner of the battle, thus advancing to the knockout rounds, where he was paired against Team Adam's Dustin Christensen, with Semple singing Foreigner's "I Want to Know What Love Is" while Christensen opted the song "Free" from Zac Brown Band, with Adam Levine choosing Semple as winner of the Knockout and moving forward to the Live Shows.

On 9 November 2015, in the first round of live shows broadcast, he sang "To Be with You", but failed to attract the top 2 votes of Team Adam finalists, and failed to be saved by Levine and was eliminated from competition on 11 November 2015.

Non Competition Performances:

Albums with 7th Heaven

• 2007: Medley CD
• 2008: U.S.A – U.K.
• 2009: Unplugged
• 2010: Pop Medley 2 (2009)
• 2010: Medley CD/DVD
• 2010: Jukebox
• 2010: Merry Christmas in Chicago
• 2011: Pop Media

Singles with One True Voice

• 2002: "Sacred Trust / After You're Gone" , (reached No. 2 in the British Singles Chart)
• 2003: "Shakespeare's (Way with) Words" (reached No. 10 in the British Singles Chart)

Albums with SEMPLE

• 2013: Not for Radio
• 2013: Live At H.O.M.E.
• 2015: Learn How to Fly
• 2016: Anytime Anywhere
• 2017: For One Night Only
• 2018: 5 O'clock

Albums with The Cyberiam

• 2018: The Cyberiam
• 2019: The Butterfly Effect
• 2019: Live in the Cyberiam
• 2020: Forging Nations Live!
• 2021: Connected