At lunch, on the second day, England were 488 for eight after Bell, who'd made 119, had relegated Kevin Pietersen (135) to an unfamiliar supporting role in an interrupted stand worth 141.
Bell was the first England batsman since Allan Lamb against the West Indies in 1984 to score hundreds in three consecutive Tests in the same home series.
The 24-year-old Bell made 100 not out in the drawn first Test against Pakistan at Lord's and an unbeaten 106 in the innings and 120-run second Test win at Old Trafford, which put England 1-0 up in the four-match series.
He fell shortly before lunch when he was bowled off-stump, trying to steer leg-spinner Danish Kaneria down to third man, having faced 206 balls with 12 fours in a four-and-a-half hour innings.
Sajid Mahmood was a Test-best 22 not out and Stephen Harmison, who pulled Shahid Nazir for two sixes in consecutive balls and swept Kaneria for four, 30 not out after the duo had added 43 in just five overs.
Their partnership set the seal on a session where England scored 141 runs.
After Lord's, Bell expected to be dropped for Andrew Flintoff but the all-rounder's ongoing absence with an ankle injury gave the right-handed batsman a reprieve.
England resumed on 347 for six with the 26-year-old Pietersen, who'd retired hurt Friday after scoring 104, facing Saturday's first ball after going off with cramp in his left forearm.
Fast bowler Umar Gul, who'd taken two wickets with the new ball late on Friday on his way to figures of four for 73 to give Pakistan a foothold in the match, opened the attack on Saturday in overcast, swing-friendly conditions.
Pietersen, who hadn't reached fifty in his previous six Test innings, began watchfully but opened up with a flamboyant cover-drive off Nazir.
Bell had a nervy moment on 80 when a Pietersen straight drive was deflected onto the stumps at the non-striker's end by bowler Gul but that was a rare moment of concern for England.
But Bell reacted quickly to dive back into his crease and, after consultation with the TV umpire, he was given not out.
Pietersen's edged four off Gul though the slip cordon down to third man brought up a century stand with Bell, who went to 89 with an elegantly guided late cut down to third man for four, also off Gul.
Bell then on-drove seamer Mohammad Sami for his 11th four to complete a stylish 172-ball hundred, his fifth Test century and fourth against Pakistan.
In 1990 Graham Gooch scored four hundreds in three successive home Tests, including a triple century, but the former captain's feat was achieved against New Zealand and India.
Pietersen on-drove Sami on the up for an audacious boundary but soon afterwards the South Africa-born batsman carelessly lofted him to Nazir at long-off, after the fielder had been pushed back.
He faced 169 balls in an innings spanning four-and-a-half hours with two sixes and 20 fours.
Pakistan, as had been the case in the first two Tests, were again finding life hard without injured fast bowlers Shoaib Akhtar, Mohammad Asid and Rana Naved-ul-Hasan.