"I am survivor of domestic violence … which is something I never expected I'd be saying," Benoist told her 3.8 million followers, revealing that the violence began five months into the relationship when her partner threw a smoothie at her face.
"The abuse was not violent at first," she said.
"There was a lot of jealousy, he was snooping on devices, he was angry when I spoke to another man, I had to change clothes often before we went out because he didn't want people looking at me," she explained, adding that the "red flags" didn't feel like abuse at the time.
"It felt like it happened on a different planet," she said of his eventual violent outbursts.
"The stark truth is I learned what it felt like to be pinned down and slapped repeatedly, punched so hard the wind was knocked out of me, dragged by my hair across pavement, headbutted, pinched until my skin broke, shoved into a wall so hard the dry wall broke, choked.
"I learned quickly not to lock myself in rooms because the door would be inevitably broken down. I learned not to value my property, I learned not to value myself," she said.
Benoist, who was previously married to Glee actor Blake Jenner, went on to explain that after many months of withdrawing herself from social situations, one particularly violent attack forced her to consider leaving her former partner with the help of a friend who suspected things were not as they seem.
News.com.au is not suggesting Benoist is referring to Jenner as her alleged abuser.
She said the alleged incident involved her ex-partner throwing his phone at her face so hard she required urgent medical attention, but she told police and medical staff she had "hit her head on a pot plant" – a story she claims they devised together.
"The impact tore my iris, nearly ruptured my eyeball, lacerated my skin and broke my nose. My left eye swelled shut, I had a fat lip," she said, adding that her vision would "never be the same".
Since her post, hundreds of fans have thrown their support behind the actress in solidarity via the hashtag #IStandWithMelissa, expressing how much they admire her courage for speaking out.
Admitting leaving her partner was "no walk in the park" the star is dedicated to helping lower the alarming intimate partner violence rates in the US, often sharing messages of support from the I Am Not OK movement and Futures Without Violence Instagram page.
"I want those statistics to change and I hope that telling my story might help more stories like mine from happening," Benoist, who married actor Chris Wood in September, said in her video message.
"I am here, I am with you and you can and deserve to live a violence-free life.
"I will be healing from this for the rest of my life … but it is possible."
If you're in danger now:
• Phone the police on 111 or ask neighbours of friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay
Where to go for help or more information:
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shakti: Providing specialist cultural services for African, Asian and middle eastern women and their children. Crisis line 24/7 0800 742 584
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz