Several thousand people were in attendance, including former Alaska Gov. Sarah Palin and her husband. Some in the somber crowd carried flower bouquets.
Many said before the service started that they didn't know the 38-year-old Kyle, whom authorities say was killed Feb. 2 at a North Texas shooting range by an Iraq War veteran.
Air Force Master Sgt. Kevin Phillips said he wasn't surprised by the large turnout. He came from his Fort Worth home to honor "a brother in arms."
"I'm here to pay my respects to him, and also for all of those who have fallen while serving this country," said Esperanza Meza, who is in the Texas State Guard.
Before and during the service, pictures of Kyle, his family and SEALS were shown on a large screen in the stadium. The back page of the memorial service program included handwritten notes from Kyle's young kids, signed "Baby Girl" and "Bubba."
Kyle completed four tours of duty in Iraq and wrote the best-selling book "American Sniper."
Kyle's funeral service is scheduled for Tuesday. He will be buried at the Texas State Cemetery in Austin after a 200-mile funeral procession.
Another Iraq War veteran, 25-year-old Eddie Ray Routh, has been charged in the killings of Kyle and his friend Chad Littlefield at a gun range. Routh is being held in Erath County on $3 million bond.
The director of the nonprofit that Kyle set up to give in-home fitness equipment to physically and emotionally wounded veterans has said that Kyle and Littlefield apparently had been helping Routh work through post-traumatic stress disorder.
Kyle, Littlefield and Routh were all together when they arrived at the shooting range at Rough Creek Lodge, about 50 miles southwest of Fort Worth, authorities say. Routh later fled the range in Kyle's truck and went to his sister's home.
According to a search warrant, Routh told his sister and brother-in-law that the men "were out shooting target practice and he couldn't trust them so he killed them before they could kill him." Routh's sister called the police, describing her brother as "psychotic." Routh was arrested after a short police chase.
Routh's brother-in-law told authorities that Routh had recently been diagnosed with post-traumatic stress disorder. One of Routh's attorneys, J. Warren St. John, said his client had been released from the Dallas Veterans Affairs hospital against his family's wishes just two days before the shootings.
Littlefield's funeral was held Friday in Midlothian, where he and Kyle were neighbors. After the funeral, Littlefield's relatives said the men's outing with Routh was intended to be therapeutic.
Littlefield's father-in-law, Tom Montgomery, said Kyle regularly took veterans to the shooting range, and that Littlefield often assisted in efforts to help veterans.