The decision was announced by WST chairman Steve Dawson during day 11 of the World Championship at the Crucible in Sheffield, an event for which seven-time champion Hendry did not attempt to qualify.
The 53-year-old from South Queenferry won just three times in 11 matches after coming out of retirement in September 2020 and accepting a two-year invitational tour card.
Doherty, who beat Hendry in the final of the 1997 World Championship, lost 6-4 to Rory McLeod in the second round of qualifying for this year's event.
Dawson said: "We have decided to offer Ken Doherty and Stephen Hendry invitational tour cards for the next two seasons.
"They are both great ambassadors for our sport and they have both done a huge amount to grow snooker around the world over many years.
"Both Ken and Stephen continue to generate interest from fans, television and media.
"We wish them all the best for the next two seasons. We will review this invitation at the end of the two-year period."
Dawson also announced that the format for November's Cazoo UK Championship in York has changed to mirror that of the World Championship, with the top 16 players seeded into the last 32 and the other 16 to come through qualifying.
Prize money has been increased to £1.2million, with the first prize up from £200,000 to £250,000.