Confession: until last night, we knew Caitlin Fitzgerald only as Libby Masters in the 1950s TV drama Masters of Sex. We didn't know her previous work, how she dressed in the modern world or how artfully she could carry off a blunt blonde bob and red lipstick. But her appearance on the red carpet for the Golden Globe Awards changed all that.

In our defence, Fitzgerald is relatively new to the Hollywood spotlight. She had minor roles in It's Complicated and Gossip Girl, but with her complex portrayal of Masters, the wife of a groundbreaking sex researcher, her career has moved up a notch. Alongside co-stars Michael Sheen and Lizzy Caplan, she glowed with confidence on last night's red carpet – and the fashion press took notice.

On the show, Fitzgerald's style is elegant, buttoned-up femininity – think Betty Draper, circa Season 1 of Mad Men. Costume design for Masters of Sex was handled by Ane Crabtree, who told an interviewer that her team had to make most of the costumes from scratch rather than sourcing vintage clothing, because the cast was so tall – Fitzgerald herself is five foot 10.

Offscreen, you can chart an evolution in Fitzgerald's style – from an initial awkwardness as she posed at New York galas and screenings, to the assured glamour she slipped into around the time of Masters of Sex's debut (September last year). Her short hair is a dramatic improvement, giving her the kind of tousled, nonchalant sex appeal that's so difficult to project with a tumbling, princess-like blowdry. And though she looks stunning in designer gowns, she's clearly drawn to a more undone, informal look – her staple fabric for casual outfits is black leather.

In a recent interview she revealed that she chooses most of her clothes herself, but has 'a couple very talented stylist friends who sometimes help me'. If they're responsible for her latest looks, she'd do well to put them on the payroll – because thanks to that Emilia Wickstead dress at the Golden Globes, she's now firmly on our radar. Click through to the gallery to track her style history.