He matched his achievement in the 50m butterfly with the same placing in the 50m freestyle event on Saturday evening.
Proud had swam 21.88 in the semi-finals to progress to the medal race. That was close to his British record. However, he did not get the same impressive start in the final and clocked 22.04.
Finishing eighth, though, was a big improvement on his 18th spot in the same event two years ago.
Proud said: “You don’t go into a race hoping you come last but to be honest I’m just happy I was in the final.
“It was a great experience. The noise before the start was immense. I’ve never seen anything like it or anything like it.”
He added: “I’m learning how to control my emotions. When I’m on the blocks I don’t think about who is around me, but when I finish, I look across the pool and see these swimmers I’ve been looking up to for years. They are my idols so to be swimming against them in a World Championship final is a great feeling.”
Meanwhile, Proud’s Leander team-mate Ruta Meilutyte has qualified fastest for the women’s 50m breaststroke final on Sunday.
She swam 29.98 in the semis, having produced a storming heat swim of 29.74 seconds just hours earlier.
After losing her 100m title on Tuesday, the 18-year-old Lithuanian world record holder appears keen to prove a point in the one-length event.
Controversial Russian 100m champion Yuliya Efimova, who beat Meilutyte to gold earlier in the week, qualified second fastest for the 50m in 30.14.