The 38-year-old Irish actress, who plays Clare Fraser on Starz's "Outsider" series, confirmed her engagement to Tony McGill at the Golden Globe Awards on Sunday.
"It happened over the break. I'm very happy," she told People on the red carpet.
Balfe wore her engagement ring on her left hand and another diamond sparkler on her right.
She was one of several stars to dress in black as a sign of solidarity with the Time's Up equality and anti-harassment campaign.
"#TimesUp @TIMESUPNOW," the star tweeted alongside a Time's Up post reading, "Why I Wear Black Today: For equity and parity across all industries. For safety among every worker in every occupation. For inclusion of all women and marginalized people."
E! News reported Balfe, who was nominated for Best Actress in a Television Series -- Drama, has been dating McGill for years.
The couple were first linked in 2015 after a friend shared an Instagram video of Balfe sitting on McGill's lap.
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