Judy Littlefield is the mother of Chad Littlefield, 35, who was with Chris Kyle, 38, when the two were shot dead on a shooting range in Texas in 2013.
Eddie Ray Routh, 27, who has schizophrenia and post-traumatic stress disorder, was found guilty of Littlefield and Kyle's murder today, and sentenced to life imprisonment with no chance of parole.
Routh admitted the killings but pleaded insanity due his mental illness.
Mrs Littlefield said: "We've waited two years for God to get justice for us on behalf of our son, and as always God has proved to be faithful, and we're so thrilled that we have the verdict that we have tonight.
The cover photo of a Facebook page devoted Chad Littlefield shows a picture of him with the words: "Trust my Lord and Savior with your life and eternity."
Chris Kyle was a former US Navy SEAL who served as an American sniper during the Iraq War.
He has been recognised as the most prolific sniper in American history according to his biography, which was the inspiration for the recent American Sniper film starring Bradley Cooper and Sienna Miller, and directed by Clint Eastwood.
Cooper received an Academy nomination for Best Actor for his portrayal of Chris Kyle, whilst Eastwood's American Sniper received an Academy nomination for Best Picture.