The London Olympic silver medallist enjoyed an excellent gate from the outside in her quarter-final to finish second.
The semifinal proved a tougher battle after she was squeezed on the outside, but Walker made a splendid move on the turn to gain three spots. She pushed into fourth spot and held off the challengers to make the finals.
Walker had a good gate in the final but ran out of real estate on the outside and was shuffled to the rear of the field, and had to be content for eighth.
The final was won by American Alise Post, a popular rider who grabbed her first world title.
It was a poignant moment with the entire field riding out to congratulate her after she had hugged fiancee and former world champion Sam Willoughby, who was paralysed in a BMX crash last year.
Walker's last world championship final was 2014 and previous to that 2011 when she finished runner-up.
"I really honestly did not know if I was going to get out of the moto stage," Walker said.
"My moto draw had three finalists in it and two others who had made World Cup finals.
"To make this final, I am really proud of myself. I still need to work on my first few pedal strokes out of the gate but my track speed was good.
"To be in the final, to get a good gate, have a good first straight, to come away in one piece - honestly this is a proud moment and a cool way for me to go through a world championships.
"I have to process this first. The field here was outstanding. There was no one missing. This weekend was very promising and I think if I can nail the first few metres out of the start, then I really think I can be right there in terms of the Olympics."
The 2018 world championships will be in Baku, Azerbaijan.