DC's Green Lanterns derive their power from their imagination and will, just like Tony Stark. His creativity and inventiveness make him an incredibly powerful Green Lantern, surpassing even DC's most powerful heroes like the JLA/Avengers crossover.
Being a Green Lantern is one of the most powerful things a person can become in the DC Universe, requiring incredible willpower and a vast amount of creativity. DC admitted that Marvel's Iron Man would be an exceptional candidate due to his exceptional combination of strength of will and boundless imagination.
Tony Stark helped Green Lantern unleash his full potential by summoning an advanced construct whose power was beyond anything Green Lantern had ever created before. This raised the question of just how powerful Iron Man would be with a power ring of his own.
Tony Stark is a genius inventor, crafting marvels that transcend the boundaries of the Marvel Universe. He has defied expectations by creating a nano-tech based Iron Man Suit, integrating symbiotic organisms with mechanical systems, and even merging Celestial technology into his suit. With his unparalleled ingenuity and creative genius, it is evident why he would be an ideal candidate for the Green Lantern Corps. Even renowned Lantern expert Kyle Raynar acknowledges in JLA/Avengers that Tony Stark's ability to conjure such an extraordinary construct within seconds was nothing short of remarkable.
There is no doubt that Tony Stark is one of the most creative individuals in the Marvel Cinematic Universe. Even when facing extreme circumstances and limited resources, he consistently finds a way to create solutions that save the day. His ingenuity and resourcefulness are unmatched, as shown in numerous instances throughout the franchise, where he single-handedly defeats powerful adversaries.