There’s a little game Meryl Streep likes to play while she exercises. “When I swim my 55 laps,” says the American actress, “I try to remember, in order, the movies I’ve been in, and I can’t… the past is just a miasma.” True, there have been a lot of them, but the point is that Streep is still so busy with new work that she has no time to order her back catalogue. Indeed, at 60, she is enjoying the most creative and successful run of films of her career – a fact confirmed earlier this month when she was nominated for two Golden Globe awards in the Best Actress category for her roles in this year’s Julie and Julia and the upcoming romantic comedy It’s Complicated, released on 8 January. This latest recognition brings Streep’s total Golden Globe nominations to a record-breaking 25, of which she has won six. This enviable position of competing against yourself for such prestigious prizes would be remarkable for any actor, but what makes Streep’s case exceptional is the shift it marks in the film industry as a whole. For decades campaigners have been complaining about the lack of good roles in movies for older women, leaving actresses over 50 to battle for bit parts or comic turns. Movie moguls, meanwhile, have argued that stories about middle-aged women just don’t make sound business sense. Streep’s recent achievements might finally change all that; first by showing that feisty, sexy central characters like Miranda in The Devil Wears Prada and Donna in Mamma Mia! could carry a film, and secondly that the result can be box office gold. Mamma Mia! has now taken more than $600m worldwide, while ticket sales for Julie and Julia, in which Streep plays the middle-aged cookery writer Julia Childs, currently stand at over $120m. Streep’s own earnings of $24m for the period June 2008 to June 2009 put her third in the ranking of the world’s highest paid actresses, behind only Jennifer Aniston, 40, and Angelina Jolie, 34. Films depend on many factors for their success, of course, not least good writing and directing, but the talent of the lead actor can make or break a movie. What is it about Streep that draws both the crowds and critical approval?

Part of the appeal, certainly, is that the facts about Streep’s private life are so scant, or have been deliberately kept to such a minimum, that we are able to believe fully in almost any character she plays. This much we know: she was born Mary Louise Streep in Summit, New Jersey, in 1949. Her father was a pharmaceuticals executive, her mother a graphic artist. She studied acting at Vassar College and Yale School of Drama before starting professional work on the Broadway stage in the mid-1970s. She quickly moved into films and gained critical attention from her earliest roles, including a part in The Deer Hunter (1978) for which she won her first Golden Globe nomination. In 1975, Streep acted opposite Godfather star John Cazale in a New York production of Measure for Measure and the pair became engaged. They appeared on screen together in The Deer Hunter and she nursed him during his terminal battle with bone cancer. After his death, she met the sculptor Don Gummer and they were married in September 1978. They have four children: Henry, 30, Mamie, 26, Grace Jane, 23, and Louisa, 18. The Gummers divide their time between a home in Manhattan and a farm in Connecticut. Streep’s three eldest offspring all now work as actors. Right from the start, Streep was determined to give her children as normal a family life as possible, making sure she was there to send them off to school and spend time with them at weekends. She also guarded their privacy fiercely. “You could argue that such a policy is for the benefit of the younger family,” says film historian David Thomson, “but it’s to the steady advantage of the actress, too, in that she seems to understand that her own work is rooted in the attentive but common sense study of how ordinary people live.”

And it is in playing ordinary women faced with extraordinary circumstances that Streep first excelled herself. In 1979 she won an Oscar for Best Supporting Actress for her memorable performance as the mother fighting for custody of her child in Kramer vs Kramer. This was followed a few years later with the Best Actress Oscar for Sophie’s Choice, the film adaptation of William Styron’s novel about a Polish prisoner of war forced to choose which of her two children should live. Streep reportedly shot the choice scene in a single harrowing take. Although she is beautiful by any standard, a classic blue-eyed blonde with trademark cheekbones, she hasn’t allowed herself to be typecast as a sex symbol. Even at the height of her physical appeal she regularly played the roles of tough, uncompromising real-life women – anti-nuclear activist Karen Silkwood in Silkwood (1983), dingo baby mother Lindy Chamberlain in A Cry in the Dark (1988) and writer Karen Blixen in Out of Africa (1985) – for whom independence and principles always came before any consideration of being attractive to men. Despite these efforts, however, Streep struggled through the entire decade of her forties playing dud roles; as a result of which it’s hard to pick out a single memorable film she made between 1988 and 2002. Perhaps the parts just weren’t there, or perhaps it’s just that nobody knew what to do with an attractive actress who was neither the youthful object of desire nor the dangerous older women. Low points during this period include a first foray into comedy in She-Devil (1989), and an ill-advised turn in Carrie Fisher’s autobiographical Postcards from the Edge. The revival of Streep’s career can be firmly dated to the two roles she played in 2002, the first as writer Susan Orlean in Spike Jonze’s kooky Post-modern drama Adaptation, the second in Stephen Daldry’s Oscar winning study of the female psyche, The Hours. It was Streep back on form in the way her public liked her best: strong, spirited, independent. Such portrayals of characters struggling against convention had already won her a large following among gay men, and then she won a permanent place in their hearts with a brilliant turn as a tolerant Mormon mother who comes to terms with her son’s homosexuality in the TV adaptation of Tony Kushner’s play Angels in America.

Streep has been on a roll ever since, ramping up her status as a gay icon to draw in extra crowds (The Devil Wears Prada and Mamma Mia! are both camp classics). But now she faces a harder test. Can she pull off the part as the lust object in the romantic comedy It’s Complicated at an age when most actresses in the past would have been playing the mother-in-law from hell? The Golden Globe nomination is an early indication that she may have succeeded, but for confirmation we will have to wait until the Oscars are announced in February. Streep has already matched Katharine Hepburn’s record of a dozen nominations for Best Actress. But it is almost 30 years since she last held a statuette in her hands on the night. Surely the time has come to confirm her position as an international treasure. For her part, Streep has already settled happily into the role. In April 2008 she sat through a gala tribute to her work at the Lincoln Centre in New York. “They were showing clips from my earlier films,” she says. “All I could see was this beautiful young woman who was anxious about whether she was too heavy or if her nose was too big. I felt like saying to her, ‘Just relax and it will all be ok’.”

Streep’s joy in her most recent roles has been palpable, and this is part of the reason she has been so enjoyable to watch. The woman David Thomson has called “the best actress we have” may never be able to get her films in order during her morning swims, but if it means it’s because she’s still working, then the pleasure will be all ours.