Well technically, Scott Travis has been their longest running drummer. But if you are referring to core members, only two remain, Halford, and Tipton (when he can play).

Well, if you are being technical “no,” but I would say “yes” and forgot him. So, three original members.

Here is how the band was started:

“Judas Priest formed in 1969 in industrial West Bromwich, in the Black Country, by lead vocalist Al Atkins and bassist Brian “Bruno” Stapenhill, with John Perry on guitars and John “Fezza” Partridge on drums. Perry soon died in a road accident, and amongst the replacements the band auditioned were future Judas Priest guitarist Kenny “K. K.” Downing; at the time, they turned him down in favour of 17-year-old multi-instrumentalist Ernest Chataway, who had played with Birmingham band Black Sabbath when they were still called Earth.[2] Stapenhill came up with the name Judas Priest from Bob Dylan’s song The Ballad of Frankie Lee and Judas Priest on the album John Wesley Harding.[3] No member of that early line-up lasted long enough to play on the band’s recordings, though several songs co-written by Atkins appeared on their first two albums.[2]

The band gained a three-album recording contract with the label Immediate in late 1969 after a gig in Walsall,[a] but the label went out of business before an album could be recorded, and the band split in 1970. Late in the year, Atkins found a heavy rock band called Freight rehearsing without a singer, made up of K. K. Downing on guitars, his childhood friend Ian “Skull” Hill on bass, and drummer John Ellis.[4] He joined them, and they took on Atkins’ defunct band’s name. Their first gig was on 6 March 1971. Ellis quit later that year and was replaced with Alan Moore. Early shows included Hendrix and Quatermass covers, and in 1972 the set list included the originals “Never Satisfied”, “Winter”, and the show-closer “Caviar and Meths”.[5] July 1971 also saw them making their first recording, a 45 of “Mind Conception” with “Holy is the Man” on the B side for the Zella Records label.[6]

Moore left and was replaced with Christopher Louis “Congo” Campbell, and the band joined Black Sabbath guitarist Tony Iommi’s management agency Iommi Management Agency.[b] Atkins continued to write material for the band—including Whiskey Woman, which became the base for the Judas Priest staple Victim of Changes—but as finances were tight and he had a family to support, he played his last gigs with the band in December 1972.[8] Campbell left soon afterwards, and the band enlisted two members of the band Hiroshima: drummer John Hinch and vocalist Rob Halford, the brother of Hill’s girlfriend.[c] Judas Priest made their first tour of continental Europe in early 1974 and returned to England that April to sign a recording deal with the label Gull.[10] Gull suggested adding a fifth member to fill in the band’s sound; they took on as a second lead guitarist Glenn Tipton,[10] whose group The Flying Hat Band were also managed by Iommi’s agency.[7] A precursor of The Flying Hat Band called Shave’Em Dry featured future Starfighters drummer Barry Scrannage, who had played with original Priest members Ernest Chataway and Bruno Stapenhill in the band Bullion.

Yes, that makes sense.

PS-I cannot take credit for that, I got the information from Wikipedia. I know the band’s history, but not every detail.