Green Lantern Ring Mastery:
Stewart's constructs are among the most powerful. The constructs he creates are never hollow, with well thought out designs.
Architecture
Firearms
Hand-to-Hand Combat (Advanced)
Indomitable Will
Leadership

Personality:
John Stewart is at heart a professional soldier, a man of duty. He takes his roles as a protector of Earth, a member of the Green Lantern Corps, and a founding member of the Justice League with the utmost seriousness. At times this has led him into conflict with comrades like the Flash or Supergirl, who do not appear to share this serious attitude. His sense of responsibility is beyond reproach, as seen during his trial in the Ajuris System; John believes that beings entrusted with great power must be held accountable for their actions, including himself.

John's long absence from his homeworld has left him with some difficulty fitting back into normal Earth society, but his experiences with the Justice League have helped him to deal with this to some degree.

Compared to some Green Lanterns (such as Katma Tui, who has taken him to task on the matter), John tends to be fairly straightforward in the use of his power ring, eschewing complicated or innovative ring-constructs in favor of simple beam-blasts or defensive barriers. John's simple, efficient approach is likely a result of his military training.

Beneath John's hard-nosed military exterior, there remains a certain (and normally well-hidden) streak of playfulness and sentimentality.