Antonio was a lead detective in Intelligence in Chicago PD, but moved to the State Attorney's office after Peter Stone approached him with a job as a Chief Investigator.
Antonio was married to Laura, who ran a bakery with their children - Eva and Diego. However, after he was shot on the job, she refused to allow him back to work. This caused an argument between the two as she did not want him back on a job she considered too dangerous. She left him with their children in the Season 1 finale of Chicago PD, after which they got a divorce and arranged joint custody assumedly.
Antonio has a sister, Gabriela Dawson, who is a firefighter and paramedic at Firehouse 51 in Chicago Fire. The two are very close.