12:07 PM PT -- The jury has just voted to sentence Carly Gregg to life imprisonment without the possibility of parole for the first-degree murder and attempted murder convictions and 10 years for evidence tampering. The judge says the sentences will run concurrently.

Carly appeared much more composed during sentencing ... no tears streaming down her face -- remaining calm while the judge explained the appeal process.

A jury has handed down their verdict in the murder trial of Carly Gregg, the 15-year-old charged with fatally gunning down her mother with a .357 Magnum in March.

The Mississippi teen was found guilty Friday of first-degree murder, attempted murder, and tampering with evidence.

As Gregg was being read her fate, she was visibly distraught ... tears welling up in her eyes while the jury filed in, looking crestfallen after she was convicted on all three of the charges against her, before breaking into sobs.

As we reported, home-security footage was shown during the week-long trial of Gregg appearing to follow her mother, Ashley Smylie, into their house ... gunshots are heard off-screen, before Gregg, who was 14 at the time, sits on a stool in the kitchen and browses Smylie's cell phone.

Gregg then reportedly texted her stepfather, Heath, to lure him to the home. He was shot and wounded in the shoulder while struggling with Carly for the gun when he arrived at the house.

The shocking video from the March 19 shooting of her mother was played Tuesday in a Rankin County courtroom during Gregg's murder trial, which has received national attention.

Prosecutors initially offered Gregg a plea deal that would've landed her in jail for 40 years ... but, she turned it down and her attorneys were pursuing an insanity defense.

On Thursday, Carly was seen in court seemingly unable to contain her laughter -- what prompted her snickering was unclear, but it happened after her lawyer wrote on a notepad.