Babar Azam celebrates a half century against New Zealand on Wednesday. Reuters
The 24-year-old reached the milestone in his 68th innings during Pakistan's chase of a 238-run target.
Babar took 11 innings more than South Africa's Hashim Amla, who reached the milestone in 57 innings, but overtook West Indies great Viv Richards (69 innings).
Pakistan were 110 for three at the halfway point of 25 overs at Edgbaston, needing another 128 runs for victory.
Babar and Mohammad Hafeez (32) added 66 for the third wicket after Pakistan lost openers Fakhar Zaman (nine) and Imam-ul-Haq (19).
Hafeez was caught by Lockie Ferguson in the deep off the bowling of New Zealand captain Kane Williamson for 32 to leave Pakistan 110-3.
Babar went on to reach his 50 off 65 balls with five fours.
Earlier, New Zealand reached 237-6 in their 50 overs, with Jimmy Neesham hitting a career-best 97 not out while Colin de Grandhomme made 64.
Left-arm seamer Shaheen Shah Afridi (3-28) starred as Pakistan reduced New Zealand to 83-5.
New Zealand were wobbling badly when the in-form Williamson was dismissed by leg-spinner Shadab Khan, who enticed the skipper into giving an edge to wicketkeeper Sarfaraz Ahmed when he was on 41.
New Zealand, who are second in the 10-team table with 11 points, kept the same team for the fifth match in a row.
Pakistan, who are seventh, with five points, also kept faith with the side that beat South Africa at Lord's on Sunday.
Sarfaraz Ahmed's side needed to smash the world record for margin of victory in a one-day international but, after winning the toss at Lord's, they failed to muster enough runs to give them a chance.
Bangladesh must be all out for seven or lower if Pakistan are to deny New Zealand a place in the semi-finals alongside Australia, India and England.
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