The British-born actor lost his battle with non-Hodgkin's lymphoma a year ago (Sep11), and he'll be remembered at the celebrity fundraiser by friends and castmates.
Lawless has shot a public service announcement driving fans to the telethon, stating Whitfield was a "true champion, an amazing man... and an inspiration to us all".
She adds, "It was an honour to know him."
Gwyneth Paltrow is masterminding this year's Stand Up 2 Cancer event, which will be held at the Shrine Auditorium in Los Angeles.
The hour-long telethon will feature Tom Hanks, Halle Berry, Justin Timberlake and Emma Stone.