A South Carolina jury has found Richard "Alex" Murdaugh guilty of killing his wife and son, convicting the once-influential lawyer of murder in a case that has gripped the nation's attention for nearly two years.

The 12-person jury declared Murdaugh, 54, guilty on two counts of murdering his wife Maggie, 52, and youngest son, Paul, 22, who were executed at close range near the dog kennels on their family estate on the evening of June 7, 2021.

He was also convicted of two related firearms charges.

Murdaugh betrayed no emotion on Thursday as the jury foreperson read the verdict, which the panel reached after three hours of deliberations.

His lawyer immediately motioned for a mistrial, which the judge swiftly denied.

"The evidence of guilt is overwhelming," South Carolina Circuit Court Judge Clifton Newman said.

Murdaugh, the scion of an influential legal family in an area west of Charleston, pleaded not guilty, though he admitted to lying about his alibi and to committing to an array of financial crimes in confessions that dented his credibility with the jury.

With the guilty verdict, Murdaugh faces 30 years to life in prison for each of the two counts of murder when he is sentenced on Friday.

The case has drawn intense media coverage given the family's immense political power in and around Colleton County, where the trial took place.

For decades until 2006, family members served as the leading prosecutor in the area, and Murdaugh was a prominent personal injury lawyer in the Deep South state.

Throughout the trial, prosecutors portrayed Murdaugh as a serial liar and argued that only he had the means and the opportunity to commit the murders.

Prosecutors said he gunned down his wife and son to distract from his financial crimes, including the theft of millions of dollars from his law partners and clients - money used to feed a years-long addiction to opioids and support an expensive lifestyle.

Among the state's strongest evidence was Murdaugh's admission from the stand that he lied about his whereabouts on the night of the killings, telling investigators he wasn't at the dog kennels before the murders.

Murdaugh changed his account after the jury listened to audio evidence placing him at the crime scene minutes before the killings occurred.

"It doesn't matter who your family is, it doesn't matter how much money you have," lead prosecutor Creighton Waters said after the verdict.

"If you do wrong, if you break the law, if you murder, then justice will be done in South Carolina."

For their part, Murdaugh's lawyers tried to paint their client as a loving family man who, while suffering financial difficulties and an opioid addiction that led him to lie and steal, would never harm his wife and child.

They floated alternative theories, with Murdaugh testifying that he believed someone angry over a deadly 2019 boating accident involving Paul likely sought revenge on his son.

But prosecutors focused on Murdaugh's credibility, returning repeatedly to his admission that he lied about something as critical as where he was when his wife and child were killed.

The judge told jurors they made the right call, saying "all of the evidence pointed to only one conclusion, and that's the conclusion that you all reached".