The southern state administered pentobarbital instead of sodium thiopental, which is no longer manufactured in the United States, along with two other drugs as the lethal cocktail to execute Cary Kerr, 46. It was the first time Texas had used the drug and the third US state to do so after Ohio and Oklahoma.
Kerr, who was convicted by a jury and sentenced to death in 2003 for assaulting and strangling 34-year-old Pamela Horton, had claimed his court-appointed lawyer did not represent him properly when appealing his conviction.
He was pronounced dead at 6:19pm (1229 GMT) on Tuesday, 16 minutes after the lethal drugs flowed, according to Texas Department of Criminal Justice.
Kerr's reaction to the chemicals was similar to most of the 466 inmates executed in Texas since 1982 under the previous drug combination.
"I am an innocent man," Kerr declared in his final words, Lyons said.
"Never trust a court-appointed attorney. I am ready, warden ... Here we go. Lord Jesus, Jesus."
His last meal consisted of meat pizza, fried chicken, lasagne, spaghetti, meat tacos, pork ribs with spicy sauce, deep fried mushrooms with french fries, a cheeseburger, a quiche and ice cream.