Davis Love III has the most career rounds, with 2,721 rounds.

most rounds under par career
Love IIICalcavecchiaHaasBrooksMayfairSlumanCookHochCouplesFaxonSindelarTwayO'MearaPavinMickelsonFurykSinghPerryFunkCinkForsmanEstesRoberts2.7k2.6k2.5k2.5k2.5k2.5k2.4k2.3k2.3k2.3k2.3k2.3k2.3k2.3k2.3k2.2k2.2k2.2k2.2k2.2k2.2k2.2k2.2k
NAMEEVENTSROUNDSTOP 10WINSMONEY
Davis Love IIIDavis Love III24112,72118021$44,944,195
Mark CalcavecchiaMark Calcavecchia23552,60614213$24,214,778
Jay HaasJay Haas24012,5101308$14,225,392
Mark BrooksMark Brooks23072,493587$9,455,442
Billy MayfairBilly Mayfair23962,475735$20,303,642
Jeff SlumanJeff Sluman23262,4661056$18,165,266
John CookJohn Cook22282,4189811$12,685,199
Scott HochScott Hoch21322,34416311$18,530,158
Fred CouplesFred Couples20862,32616215$22,814,253
Brad FaxonBrad Faxon21702,324888$17,769,250
Joey SindelarJoey Sindelar22462,311837$11,196,462
Bob TwayBob Tway21562,2991038$15,785,814
Mark O'MearaMark O'Meara21322,28211916$14,325,370
Corey PavinCorey Pavin21722,26910815$16,021,370
Phil MickelsonPhil Mickelson17742,26019845$94,690,661
Jim FurykJim Furyk18242,24218817$71,479,894
Vijay SinghVijay Singh18912,22018534$71,236,216
Kenny PerryKenny Perry20732,21610414$32,123,129
Fred FunkFred Funk19982,214938$21,310,436
Stewart CinkStewart Cink16702,1891028$41,757,459
Dan ForsmanDan Forsman19932,178645$8,687,983
Bob EstesBob Estes20422,172914$21,628,538
Loren RobertsLoren Roberts20392,155948$15,154,767
Hal SuttonHal Sutton20572,15412414$15,267,686
Scott VerplankScott Verplank18412,116935$27,500,226
StatMuse has season-level data for rounds going back to the 1979-80 season.