Geoffrey James "Geoff" Nicholls (28 February 1948 – 28 January 2017) was a British musician and keyboardist who, until 2004, was best known as the longtime member for the heavy metal band Black Sabbath.

Nicholls also played in the NWOBHM band Quartz before joining Black Sabbath. In the late 1960s/early 1970s, Geoff played lead guitar for the Birmingham band Johnny Neal and the Starliners.

Nicholls was originally brought in as a second guitarist when Black Sabbath doubted whether they would even continue under that name. Nicholls then switched to bass when Geezer Butler left briefly, and then became the band's keyboardist upon Butler's return and the decision to keep the Sabbath name. Nicholls' first appearance on a Black Sabbath album was on 1980's Heaven and Hell, and was credited as keyboardist on every Sabbath release from that time until 13, although he was not an official member until 1986. He remained an official member until 1991, then regained member status from 1993 to 1996. He was an unofficial member once again since the reunion with Ozzy Osbourne in 1997. Although his main role with Sabbath has been on the keyboard Nicholls also played some rhythm guitar on the reunion tours, e.g. during Iommi's solo in "Snowblind" and a few tracks during the Headless Cross and Forbidden tours.

In addition to not always being credited as a full member of the band, Nicholls has rarely appeared on stage proper during Sabbath shows, instead usually playing from a side-stage or backstage position. One exception to this was the tour in support of the 1986 album Seventh Star, where he played on stage as an equal member of the band. Another is a concert in May 1988, where Nicholls played bass for a charity function.

Nicholls' involvement with the band ended when Adam Wakeman (a member of Ozzy Osbourne's solo band) was chosen to play keyboards during Sabbath's 2004 and 2005 tours as part of Ozzfest and Scott Warren (Dio) handled keyboard duties on the 2007 Heaven and Hell tour.

Until his death, Nicholls played keyboards with former Black Sabbath singer Tony Martin in his band Tony Martin's Headless Cross. Nicholls had previously performed on both of Martin's solo albums and their support tours.

Nicholls died from lung cancer on 28 January 2017 at the age of 68.