The ex-wife said she met Omar Mateen online about eight years ago and decided to move to Florida and marry him, Independent.co.uk reported.
At first, the marriage was normal, she said, but then he became abusive.
"He was not a stable person," said the ex-wife, who spoke on the condition of anonymity because she feared for her safety in the wake of the mass shooting.
"He beat me. He would just come home and start beating me up because the laundry was not finished or something like that."
While the FBI has not identified Mateen publicly, US law enforcement officials said his identification was found on the body of the suspected killer who was armed with a handgun and an assault rifle.
Mateen's ex-wife said his family was from Afghanistan, but her ex-husband was born in New York. His family later moved to Florida.
She said she was having a difficult time when she first met him and decided to move to Florida to be with him. The two married in March 2009 and moved into a two-bedroom condominium in Fort Pierce, Florida that Mateen's family owned.
"He seemed like a normal human being," she said, adding that he was not very religious and worked out at the gym often.
She said in the few months they were married he gave no signs of having fallen under the sway of radical Islam.
She said he owned a small-caliber handgun and worked as a guard at a nearby facility for juvenile delinquents.
"He was a very private person," she said.