Rachel McAdams' biggest successes have been The Notebook (2004) and The Vow (2012), weepy romances that you need a full pack of tissues to get through.

Although millions swooned when she smooched Ryan Gosling and Channing Tatum in the two movies, many dismissed her as just another pretty face - the criticism reinforced by her supporting roles in films such as Wedding Crashers (2005), where she functioned as little more than eye candy.

With her new television series True Detective, however, critics are sitting up and taking notice - the prestige crime drama, which is in its second season, is earning the 36-year-old Canadian actress some of the best reviews of her career.

Speaking to reporters in Los Angeles about her new film Southpaw - also a drama with a harder edge - McAdams confesses that she has wanted to switch things up for a long time.

"That's part of the fun - trying to have as diverse a career as you possibly can," she says.

The main stumbling block is that these opportunities are few and far between.

"These parts don't come along every day - I wish they did. There's sort of a lack of them out there," says the star, who was once dubbed Hollywood's next big thing but whose career has stagnated in recent years, a fact exacerbated by the dearth of substantive female roles in studio films.

Pickings are not quite as slim in television, which may be why movie stars, including McAdams, are migrating to the small screen.

After bit parts in big films such as Sherlock Holmes: A Game Of Shadows (2011) and Midnight In Paris (2011), landing a lead role in True Detective - an anthology series whose first season was one of the most buzzed about TV shows last year - felt like a coup.

"I don't know how I got it, but I rejoice all the time," says the actress, who is reportedly dating her 34-year-old True Detective co-star Taylor Kitsch.

For McAdams, whose breakout role was playing one of the titular villains in Mean Girls (2004), the opportunity to sink her teeth into something grittier was long overdue.

"Funnily enough, it didn't feel dark when I was doing True Detective. It was so creatively satisfying that I went home feeling quite light on my feet at the end of every day."

Compared with the TV show, the boxing drama Southpaw may seem like a return to her past movies as she once again plays the love interest in a tearjerker.

But the actress explains that she was drawn to the toughness of her character Maureen, the wife of boxer Billy (Jake Gyllenhaal).

McAdams felt the character was different from anyone she had portrayed before.

"I think Maureen felt like she was the front line for Jake's character, so everybody had to go through her. So it was great to always be that fierce, to be that mama bear with her cub. And interesting to explore where that came from," she says.

She went above and beyond in preparation for the role, deciding to learn how to box even though her character never has to.

"I figured Maureen would know a lot about the sport because she and Billy have been together for 22 years and he's been doing this for most of their life together.

"So I think she would want to know the ins and outs and every move of his - when he was out of sync, when he was on form. And I wanted to understand how physically difficult it is," says McAdams, who was coached by the same trainer as Gyllenhaal.

She ended up falling in love with boxing and kept it up after filming ended, even using it to prepare herself for her True Detective role.

"It's a fascinating sport and now I have much more respect for it and realise the incredible sacrifice that goes into being a boxer at any level.

"And," she says with glee, "I have my own gloves now."

•Southpaw is in cinemas in Singapore.