The four-year-old was partnered by Mark Zahra on his first Australian outing, claiming a fast-finishing second place in the Herbert Power Stakes at Caulfield just under two weeks ago.
Williams teamed up with Wall Of Fire in a workout with stablemate Mask Of Time at Weribee International Horse Centre on Tuesday morning and Palmer has moved to secure the rider's services in the Group One feature.
The trainer tweeted: "Delighted to confirm that Wall Of Fire will be ridden by Craig Williams in the Melbourne Cup after the pair cantered together today."
Williams felt Wall Of Fire had recovered well from his first Australian start and was pleased with his workout.
He told www.racing.com: "All I can say is that he came through the race extremely well, he is quite fresh and he wanted to really get on with his job a little bit this morning."