Thompson climbs from number five in last year's list to take the top spot. Her placing recognises her contribution in a year in which Camelot registered a 5.2% growth in lottery ticket sales and declared its intent to bid for a third National Lottery licence.
Thompson leapfrogs last year's number one, Tesco's Tim Mason, who drops a place following his relocation to head the retailer's expansion into the US.
With former PepsiCo supremo Martin Glenn dropping out of the Power 100 after quitting earlier this year, Carphone Warehouse boss Charles Dunstone moves up to number three, with WPP chief executive Sir Martin Sorrell retaining fourth place.
Marks & Spencer chief executive Stuart Rose completes the top five, having led a resurgence in the retailer's fortunes, jumping from 53rd place in 2005.
This year's Power 100 featured 19 female marketers, one fewer than last year. There were 36 new entries, the result of a number of major job changes in the past 12 months.
Power 100, page 32.