The 36-year-old achieved the feat after finishing in the top 30 behind American Sam Burns in the Sanderson Farms Championship in Mississippi on Sunday.
That took his career earnings on the US circuit to $15,517,045 from 243 events, becoming just the 133rd player to pass the $15m mark.
Knox, who hails from Inverness but has been based in Florida since attending Jacksonville University, enjoyed the biggest pay-day of his career when winning the 2015 HSBC Champions in Shanghai.
That was worth around $1.4m while he then picked up $1.18m for winning the Travelers Championship in Connecticut the following year.
Laird, who defends his Shriners Hospitals for Children Open title in Las Vegas this week, sits 94th on the all-time PGA Tour money-list with career earnings of $19,563,395.
The list is topped by Tiger Woods with $120,851,706, followed by Phil Mickelson ($94,847,060) and Dustin Johnson ($72,594,310).
Rory McIlroy sits sixth with $57,519,984 while current world No 1 Jon Rahm has already accumulated $29,775,822 in his short career.
Meanwhile, the European Tour campaign will conclude with a Dubai double-header for the second season running later this year.
It follows the addition of the $1.5m AVIV Dubai Championship to the 2021 schedule on 11-14 November on the Fire Course at Jumeirah Golf Estates.
The event, won last year when it was held as the Golf in Dubai Championship presented by DP World by Frenchman Antoine Rozner, will take place the week before the DP World Tour Championship, which will bring the curtain down on this year’s Race to Dubai on the neighbouring Earth Course.
It replaces the cancelled Nedbank Golf Challenge Hosted by Gary Player in South Africa, which will now return for its 40th anniversary in 2022.
The AVIV Dubai Championship forms a new-look end to the European Tour’s 2021 season following the recent additions of the Mallorca Golf Open (21-24 October) and Portugal Masters (4-7 November).
“It means we will have two strong ‘Swings’ to end our 2021 campaign – the Iberian Swing in Spain and Portugal and now this Dubai double-header at Jumeirah Golf Estates,” said European Tour chief executive Keith Pelley.