AUSTIN, Texas (Reuters) - Texas executed a mentally retarded convicted murderer on Tuesday after the U.S. Supreme Court refused to intervene a decade after it banned executions of such people as cruel and unusual punishment.

Marvin Wilson, 54, was convicted of the November 1992 murder of a 21-year-old police drug informant, Jerry Robert Williams, and was sentenced to death in April 1994.

Wilson had challenged his execution as unconstitutional under a 2002 Supreme Court ruling that banned executing mentally retarded people but gave states some discretion in deciding who qualified for protection.

"The application for stay of execution of sentence of death presented to Justice Scalia and by him referred to the Court is denied," the court said in an order earlier on Tuesday evening.

Justice Antonin Scalia handles emergency appeals from the 5th U.S. Circuit Court of Appeals, which oversees Texas.

Wilson was pronounced dead at 6:27 p.m. local time, according to Jason Clark, a spokesman for the Texas Department of Criminal Justice.

"Y'all do understand that I came here a sinner and leaving a saint," Wilson said as part of his final statement, according to Clark. "Take me home, Jesus, take me home, Lord, take me home, Lord."

Wilson's IQ had been measured as low as 61, below the 70 level sometimes used to delineate mental retardation. Texas argued that the test pegging Wilson's IQ at 61 was conducted by an inexperienced intern, and that several other tests showed an IQ above 70.

The state also said it had discretion under the 2002 Atkins v. Virginia ruling to consider seven factors in determining whether someone like Wilson should be executed, including his ability to lead, his ability to lie, and whether family and friends thought he was mentally retarded.

Lawyers for Wilson countered that this allowed the state to effectively ignore the Atkins ruling by unreasonably applying "non-clinical" factors to disqualify Wilson from its protections.

Texas is the only state to use such a test, Wilson's lawyer, Lee Kovarsky said.

"Whatever was in his past, the Marvin I knew was a simple man who loved his family and his god," Kovarsky said in an email on Tuesday.

"I hope that, at the very least, something like this occasions some serious reflection on what it means to be culpable. As a society, we do a decent job of sorting right from wrong, but, when we calibrate blame, it's like we're blindfolded and throwing darts," he added.

In a separate death penalty case on appeal to the Supreme Court, Chester v. Thaler, the American Association on Intellectual and Developmental Disabilities said Texas' test relies on false stereotypes and would count only the most severely incapacitated people as mentally retarded.

Texas has conducted roughly three out of every eight executions since 1976, when the Supreme Court allowed the practice to resume after a four-year hiatus, according to the Death Penalty Information Center.

Wilson was the seventh inmate executed in Texas this year and the 25th executed in the United States this year, according to the information center.

(Reporting by Terry Baynes and Jonathan Stempel in New York and Corrie MacLaggan in Austin, Texas.; Editing by Cynthia Johnston and Stacey Joyce)