Meghan has reached "the pinnacle of the greasy pole", according to the society magazine.
She trumps Commons Speaker John Bercow MP, who is at number two on the list, and model Jerry Hall, who came third.
Describing the duchess's "A-list ascent", Tatler said: "Not quite a rags-to-riches tale (she was privately educated and her scapegrace father won an Emmy for lighting direction) but the
Ralph & Russo-clad beacon of change has found a role that suits her to perfection: a tungsten toughie to drag the royal family into the 21st century."
Of Mr Bercow, the magazine said: "Notoriously fond of taxis, perhaps because his dad drove one. Now so great (if not so good), some wonder if he'll ever relinquish his Commons Speakership."
Hall is hailed for her rise from the daughter of an alcoholic Texan trucker to partner of Bryan Ferry and Mick Jagger, saying this was capped by marrying billionaire media magnate Rupert Murdoch.
Other notable figures on the list include Turner Prize-winning artist Keith Tyson, who married Murdoch's daughter Elizabeth and new John Lewis chairwoman Sharon White.
See the full feature in the October issue of Tatler, available on newsstands and digital download now.