The U.S. Supreme Court has cleared the way for the execution of a Texas death row inmate whose lawyers say is ineligible for the death penalty because of his low IQ.

Marvin Wilson is scheduled for execution Tuesday evening.

Lower courts had sided with state attorneys who questioned the validity of a psychological test that pegged Wilson's IQ at 61, below the threshold of 70 that would suggest he's mentally impaired.

Wilson's lead attorney, University of Maryland law professor Lee Kovarsky, says that if Texas proceeds with the execution, Wilson would be the lowest-IQ Texas prisoner put to death despite the Supreme Court ruling that banned the execution of mentally impaired inmates.

The 54-year-old Wilson was condemned for killing a police informant two decades ago in Beaumont, about 80 miles east of Houston.