Walker was a priest on his home planet of Astonia (with a wife and two children), which was doomed, as its ancient sun was dying. Saint Walker manages to calm his despairing people and give them hope in the face of extinction, which causes a Blue Lantern ring to choose him as a member of the Blue Lantern Corps, stating that he "has the ability to instill great hope". With his ring, he sets his sun's age back 8.9 million years, thereby saving his home planet. Saint Walker and his fellow Blue Lanterns are first introduced in the midst of the Final Crisis event as part of the build-up to the Blackest Night storyline. During the Final Crisis, Hal Jordan and John Stewart of the Green Lantern Corps have just been ambushed by the Red Lantern Corps, who take the rogue former Green Lantern Sinestro from their custody. After Jordan is injured during the conflict, his wounds are healed when he first comes into contact with Saint Walker.
In the Blackest Night storyline, having joined Hal Jordan's and Indigo-1's efforts to rally one member of each Corps to attempt to destroy the Black Lantern power battery, Saint Walker agrees to use his power ring to ease Larfleeze's hunger while they work together. When deputizing an Earth hero to assist in the current crisis until the rest of the Blue Lantern Corps can arrive, Walker's ring selects Barry Allen as a temporary Blue Lantern. After Nekron is defeated, Walker works with Carol Ferris to heal Mera of the influence of her red power ring.
In Justice League of America #55 (2011), the character joins the titular team in battling Eclipso, and attempts to assist the resurrected Hank Henshaw against Doomsday on Batman's orders.
In the War of the Green Lanterns storyline, Saint Walker and the rest of the New Guardians make their way to the planet Ryut. Krona and the Emotional Entities are nowhere to be found but the group does come upon the Book of the Black. When former Sinestro Corps member Lyssa Drak appears, she quickly subdues the New Guardians, trapping all but Hal in the Book of the Black. Hal escapes with the rings of the New Guardians, later passing Walker's ring on to Kyle Rayner when Krona infects the Central Power Battery with Parallax to bring the Green Lantern Corps under his influence. In the final battle Saint Walker is freed from the book by Kyle, his blue ring returns to him and the Guardians of the Universe then teleport him back to Odym. Afterwards, Saint Walker returns to Oa to restore Ganthet's missing hand.
In the new series Green Lantern: New Guardians, Saint Walker assisted Kyle Rayner when he became a "magnet" for other power rings, helping Kyle escape the attacks of the other four Corps members who had tracked the rings. They travel to Oa to try and seek the aid of the Guardians. Unfortunately, this plan backfires when it is revealed that Ganthet has been stripped of his emotions by the other Guardians, to the extent that he attacks Walker when Walker tries to help Kyle directly after he is briefly overwhelmed by the rings. Ganthet proclaims that the Blue Lantern Corps were a mistake that he will now rectify. After they are forced to escape the Guardians, Walker heals Arkillo's severed tongue using an illusion of Sinestro. However, in the subsequent confrontation with Archangel Invictus, Walker is unable to heal Invictus' anger at the Lanterns, although his actions do help Invictus see that the Lanterns are not completely tainted. Returning to Odym to regroup after Invictus releases the New Guardians only if they agree to kill Larfleeze, Walker learns that Odym is being attacked by the Reach, enemies of all ring-wielders, forcing him to call the other New Guardians for help when he attempts to teach the other Blue Lanterns how to channel their auras to increase their offensive capabilities so that they can fight on their own. Although he and the other New Guardians aid Kyle against Invictus, the team splits up after learning that Sayd was responsible for drawing the rings to Kyle as part of a plan to assemble a team to save Ganthet, feeling that her actions have tainted the team before it began, regardless of her motives in bringing them together.
Saint Walker possesses a blue power ring which is fueled by the emotion hope. While hope is the most powerful of the seven emotions, he must be near an active Green Lantern's power ring to tap into his own ring's full power. Otherwise, the rings are only capable of the default abilities of flight and a protective aura. This is due to the fact that the power of hope is nothing without the willpower to act on it. Blue rings must be fueled by true hope in order to operate at their users' command. While under the influence of a nearby green power ring, Saint Walker can heal wounds. The ring's power can be supplemented with the hope of other living beings; for instance, Saint Walker and Warth were able to reduce a dying sun's age by 8.6 billion years because of the hope emanating from the inhabitants of a nearby planet. A blue ring can negatively impact the performance of rings on the opposite side of the emotional spectrum. During his initial meeting with the JLA, Saint Walker discovered that his abilities can also be augmented by proximity to Starman (Mikaal Tomas). As the first and most experienced Blue Lantern, Walker has shown the ability to channel his aura to increase his strength and hold his own in a fight against some adversaries, although his powers are limited to simply strengthening his force field to a greater density around himself, and he still requires a Green Lantern to be present to actually generate constructs.
Saint Walker appears in the Green Lantern: The Animated Series episode "Lost Planet," voiced by Phil Morris. In the episode, Saint Walker is introduced as a hermit who lives on Mogo, a sentient planet that traps evildoers. He encounters Razer, a former member of the Red Lantern Corps, and tries to convince the youth to turn away from the path of violence he currently walks. Despite his peaceful demeanor, Walker is portrayed as a very agile and adept fighter, capable of disarming Razer in hand-to-hand combat without the use of a power ring. Although in possession of a green power ring, he declines joining the Corps, believing that his own destiny lies elsewhere. During "Invasion" Saint Walker talks to Mogo about what his role is in the Red Lantern invasion (as Mogo saved him and told him there is a beacon of hope that can stop the Red Lanterns) so Mogo tells him that he must climb to the highest peak of the sentient planet. As he climbs, he witnesses Atrocitus recruit one of the prisoners Mogo kept on his surface. Saint Walker wanted to exact revenge on them after they destroyed his homeworld but Mogo insisted that they were not important at that time. Once he reached the peak, he asked Mogo where the beacon was and while he thought that the empty peak was a message that there was no hope, Hal Jordan's Green Lantern power battery (now a Blue Lantern power battery thanks to Ganthet) presents Saint Walker with a Blue Power Ring and the role of being both the leader of the Blue lantern Corps and the universe's last hope. In the season finale, Saint Walker (now a Blue Lantern), along with Mogo, aid Kilowog in the final stand against the Red Lantern fleet of ships.