Tomar was a scientist on the planet Xudar before joining the Green Lantern Corps. He became a pivotal member of the Corps, training new members, like Arisia, and serving in the Honor Guard. He investigated reports of abuses of power by Sinestro on Korugar. He was close friends with Abin Sur, Green Lantern of neighboring sector 2814. He was also the first Lantern to meet Sur's replacement, Hal Jordan, and the two got along equally well. In the Post-Crisis timeline, that friendship is deepened further in that the rookie Jordan met him soon after being recruited. Jordan was brought to him by his power ring to help with his difficulties with handling the weapon and Tomar-Re not only guided the Terran to GLC headquarters for the optional training program, but also provided valuable emotional support during this difficult time.
Tomar's most famous mission while serving in the Corps dealt with the planet Krypton. Krypton, a planet in sector 2813, was growing increasingly unstable. It was due to explode, caused by internal pressures deep inside the planet's core. Tomar Re sought to use a rare compound called stellarium to absorb some of the tectonic pressure, thus saving the Kryptonians. He gathered the compound, and was en route to Krypton when a yellow solar flare blinded him, and forced him to drop the stellarium. He quickly recovered, but discovered he was blind. He gathered what little stellarium he could without his sight, and proceeded towards Krypton. He was closing in when his vision started to clear. The first thing he saw upon his sight returning was Krypton exploding. The Guardians recovered Tomar and brought him back to Oa, where he healed and rested.
He later grew to an honored senior member of the Corps, but his later career was not without cost. The most difficult moment was during the Nekron crisis when the death god used the spirit of Tomar-Re's deceased father to attempt to sway the Lantern to surrender. Although tempted, Tomar kept to his oath and destroyed his father's spirit to continue the battle, much to his personal anguish.
Tomar was retired when the Anti-Monitor sought to conquer the multiverse. He still served alongside the Corps, including John Stewart, who had become the GL for 2814. The war against the Anti-Monitor would be Tomar's final fight, as he was killed by the villain known as Goldface. Before his death, Tomar Re selected Stewart to be his replacement, thus forcing John's ring to go to Jordan, who had resigned from the Corps, thus returned him to the organization (Green Lantern vol. 2, #198).