The 28-year-old, who celebrated six months of sobriety earlier this month, turned heads in a stunning one-shoulder off-white trumpet style gown, which contrasted beautifully with her striking chocolate brown hair.
The Hostage star posed for photos as she showed off her huge lion tattoo on her upper arm in a stunning floor-skimming gown, which featured an elegant sweetheart neckline and asymmetrical tulle overlay, nipped in waist and a romantic trumpet style skirt.
The silhouette was an ideal choice for the actress, who wore her dark hair in a pretty one sided up 'do, balancing the dress beautifully.
The actress was taking on an important role when she appeared as the bridesmaid for pal and former Dancing with the Stars colleague Peta Murgatroyd, who tied the knot with fellow dancer Maksim Chmerkovskiy at the fairytale Oheka Castle (the location for Taylor Swift's "Blank Space" music video) in Long Island on Saturday.
Bride Peta looked every inch the modern princess in a stunning full ball gown which featured a tumbling ruffle skirt - a signature style of the bride's preferred designer Monique Lhuillier.
Rumer and her fellow bridesmaids also seemed to be sporting dresses from Monique Lhuillier's bridesmaid line, which tied in perfectly with the overall glamorous tone of the day.
Actress Rumer seemed to be in a better place than in recent years, and looked to be beaming while celebrating her new-found sobriety and putting her years of suffering at he hands of bullies behind her.
The star famously broke down when she appeared on the U.S hit show Dancing with the Stars, which she went on to win in 2015, when she opened up about her torment at the hands of bullies who she said made fun of the way she looked.
'Twas truly a fairytale. Congratulations @maksimc & @petamurgatroyd! We are over-the-moon that we had the honor to be apart of your magical #wedding. To many, many years of #love, light and happiness! Cheers to the #brideandgroom! #chmergatroydwedding @nicolevolynets . . . #shakeandsharemedia #maksandpeta #photobooth #photoboothnyc #dwts #ohekacastle #nywedding #happycouple #fairytale #fairytalewedding #petamurgatroyd #maksimchmerkovskiy #dancingwiththestars #nyc #nyphotobooth #happy #bride #groom #weddingplanner #eventplanner #eventprofs
Rumer also recently revealed on Instagram that she had been sober for six month as of July 2017.
“Yesterday I celebrated 6 Months of Sobriety," she said.
“It’s not something I planned on but after the long journey of getting here I can honestly say I have never been more proud of myself in my entire life.
Thank you all for the love and support and remember to be gentle with yourself.”
I will be the first one to say I'm not perfect and I mess up sometimes and every once in a while I get it right but I wanted to share this because I am really proud of myself. Yesterday I celebrated 6 Months of Sobriety. It's not something I planned on but after the long journey of getting here I can honestly say I have never been more proud of myself in my entire life. Thank you all for the love and support and remember to be gentle with yourself