Gillan had formed a songwriting duo with Episode Six's bassist Roger Glover, who was also invited to join Deep Purple and replace Nick Simper.

[1] The band was considered an underground act in the United Kingdom, but word of their success in America had influenced their reputation at home, as they gradually rose in popularity and request.

[1] A few days after their US tour, Deep Purple settled in with their usual producer Derek Lawrence at De Lane Lea Studios in Kingsway, London, already used for The Book of Taliesyn sessions, to compose and record new songs and solve the new single problem.

[1] The instrumental "Wring That Neck" from their previous album was the B-side of the British edition of "Emmaretta", which was issued in February 1969 and promoted by Deep Purple in their first full UK tour.

[10] The band's management organized the spare time from the UK tour to record new songs for a third album over the course of February and March 1969 at De Lane Lea Studios, with Lawrence as producer and Barry Ainsworth as sound engineer.

[14] The short instrumental "Fault Line" was inspired by an earthquake that the band had experienced while in Los Angeles and featured Paice's drum patterns reversed and double tracked.

[29] On Deep Purple Lord still had a great influence, which found maximum expression in the harpsichord-flavoured "Blind" and in the orchestral section of "April",[27][30] an original piece for choir and string quartet that he composed despite being hard at work in writing and arranging his Concerto for Group and Orchestra.

[26] The label ran into difficulty over the use of the Museo del Prado-owned painting, which was incorrectly perceived in the US as being anti-religious, featuring immoral scenes, and was thus rejected or poorly stocked by many record shops.

[10][36][37] Deep Purple were the label's most successful artist, but the band had not been able to produce another hit single like "Hush"[10] and their latest release "Emmaretta", out just in time for their second US tour in April 1969, was also largely unsuccessful and failed to affect the US charts.

[38] The label's financial distress caused a delay in the printing of Deep Purple, which was released in the US only in June 1969, after the band had returned home having completed their US tour.

[39] The album was released in the UK in September 1969 on EMI's sub-label Harvest Records, around the same time as the much-hyped event Concerto for Group and Orchestra held at the Royal Albert Hall in London.

[43][44] The only other international reissue of the album is the Remastered 2000 CD edition by EMI, which contains versions of "The Bird Has Flown", "Emmaretta" and live performances taken from BBC Radio sessions as bonus tracks.

[37] Thus, in early April 1969 Deep Purple were on their way back to the US to start off a two-month coast-to-coast tour as headliners which, similarly to what had happened in Britain, brought them mainly to small clubs and colleges.

[38] In fact, the band experienced some economic limitations during the tour and asked their manager John Coletta to fly back home, so the hotel bills would be reduced.

[38][46] In particular the latter had found a way to short-circuit the original Leslie speakers of his Hammond C-3 organ and connect the instrument directly into the stacks of Marshall amps, obtaining a roaring sound and matching the guitar in loudness.

[51] Meanwhile, Lord and Blackmore were tired of being identified as a "clone of Vanilla Fudge"[47] and were starting to yearn for a sharper, rawer and overall heavier sound, similar to that introduced in Led Zeppelin's debut album,[3][49][52] which had become a great success on both sides of the Atlantic, after its release in January 1969.

[50][55] Tensions were also high with bassist Nick Simper,[38] whose playing style was considered, in Paice's words, "stuck in the late '50s and early '60s" by the other band members and unfit for the new musical direction they wanted to pursue.

[59] Meanwhile, the search for a new singer to replace Evans began and Blackmore asked for help in this task from his old acquaintance Mick Underwood, at the time drummer of the British rock band Episode Six.

[60] Gillan, who did not see a future in his then current band,[60] was enthusiastic about joining Deep Purple and involved bassist Roger Glover, with whom he formed a songwriting duo.

[61] Gillan convinced the reluctant Glover to audition for Deep Purple and the two soon found themselves torn between the new band, which gladly welcomed both of them, and obligations with Episode Six for the completion of a UK tour.

[39] In between gigs all over the country, Deep Purple had rehearsed the song "Hallelujah" with Evans and Simper to be released as a new single, but it was recorded in secret on 7 June by the fresh Mark II line-up at De Lane Studios instead, with Glover still acting as a session musician.

[41] The single "Hallelujah" was released in late July in the US and the UK and featured an edited version of "April" as B-side, the final original appearance on vinyl of the Mark I formation.

[66][67] Tetragrammaton's financial problems were partially to blame, for promotion was lackluster, but the lack of a hit single to be aired on FM radio or a tour in support of the album were also important factors.

[10][68] At the time of release, Deep Purple was generally ignored by the British music press, more focused on the eventful Concerto for Group and Orchestra than on an album by an extinct line-up.

"[24] David Bowling, in his Blogcritics column, reviews the album as "the least satisfying of their three early career releases, although it can also be considered their most adventurous" for its "meandering through a number of different styles and sounds."