The first place Margot Heller worked in Camberwell is now a hairdressers, although at the time it was offering contemporary art, not cut and blow-drys. The Giray Gallery didn't last long and Heller moved on, but she returned to the area eight years ago as the director of a far more established venue, the South London Gallery (SLG).

The SLG has its roots in a working men's college established in 1868 and the building it now occupies first opened in 1898. More than 100 years later, work has just started on a £1.6m scheme to create new galleries, an apartment for artists' residencies, a cafe and an education space.

The project, which will open in 2010, will double the existing floor space and is centred on the redevelopment of an empty three-storey house next to the gallery.

Heller says the building next door was semi-derelict so one option was to knock it down and create an iconic building and perhaps divert the main entrance of the gallery to that building. "Our entrance is beautiful but does not shout 'gallery, we are open, come in'.

But what people really love about this gallery is its character. It's still got this feeling of being a real gem and has this secret garden sense where you walk down the corridor and it opens out into this very beautiful double-height space."

Heller was also keen for the extension to retain the domestic feel of the terraced house. "I wanted to keep it as a house because there are fewer and fewer art galleries in domestic spaces, whereas I have always really enjoyed exhibitions in domestic environments. It also continues that idea of a sense of discovery; so you will go into a very unassuming-looking terraced house and again there will be a very lovely looking double-height space."

The redevelopment of the gallery is the culmination of the Heller's gradual expansion of the SLG since she joined in 2001. She followed in the footsteps of David Thorp, the previous director who refocused the gallery more towards contemporary art. Thorp, who is now a freelance curator, staged a number of high-profile exhibitions by artists such as Gilbert & George, Tracey Emin and Gavin Turk.

When Thorp left in 2001, his legacy to Heller went beyond the gallery's growing reputation for contemporary art. He had also made the first moves towards making the SLG independent from the London Borough of Southwark. The gallery had been a public body since 1904, when it was taken over by London County Council, but becoming independent made sense for financial and governance reasons, as Southwark was the sole trustee.

"There was a real feeling that the gallery could raise more funds if it was independent," says Heller. "And there was a sense that if you don't have a board of trustees who are very actively involved in an organisation it is really quite vulnerable."

Achieving independence

By the time Heller joined, Thorp had secured a £30,000 stage one grant from the Arts Council Stabilisation Programme, a scheme to help arts organisations become financially stable. Heller followed this with a successful bid for £416,000 under a stage two stabilisation grant and independence was achieved in 2003. Independence has meant Southwark has nowhere to show its art collection.

The SLG is now one of Arts Council England's regularly funded organisations, which provides about 50-55 per cent of its income. Heller has increased the number of staff from five to 15, with some of the new people working on its ambitious education programme.

On the governance side, Heller now has a board of trustees that includes Matthew Slotover, the director of the Frieze Art Fair, the architect David Adjaye and Rebecca King Lassman, the former head of development at the Serpentine Gallery. Other notable achievements include a 2002 show by Keith Tyson, who went on to win the Turner Prize in the same year.

"It has been challenging but it has been exciting," Heller says. "There has been a slow and steady growth in the gallery since I started. Independence has enabled us to really up the ante in raising funds from other sources."

Heller seems to have kept a relatively low profile in the media and she admits to not finding dealing with journalists particularly easy. But Sandy Nairne, the director of the National Portrait Gallery and chairman of the steering group that helped move the SLG towards independence, says lots of people in the art world, himself included, admire what she has done at the gallery.

She was chosen to be a Turner Prize judge in 2006 and has also served two terms on the Government Art Collection Committee.

From the Tate to Southampton

Heller already had a wide range of experience when she joined the SLG. She took a job at the Tate as a secretary after the Giray Gallery closed and, although she was not there very long, she says it fired her interest in contemporary art. Heller left the Tate in 1989 to become an assistant curator at Southampton City Art Gallery, and it was there that she really cut her teeth in the contemporary art world.

The gallery was a very active collector of contemporary works and in the 1970s and 1980s was advised by the late David Brown from the Tate. "Southampton City Art Gallery was a wonderful place," says Heller. "It was a fantastic opportunity for me to be able to work on acquiring art for the collection relatively early in my career."

Heller soon became acting curator at Southampton, then curator before being appointed director aged 29. As well as working on acquisitions, buying works by artists such as Rachel Whiteread and Michael Craig-Martin, there was also a £3m redevelopment to oversee.

"The refurbishment meant I could completely rehang the galleries, which again was a wonderful opportunity, and I took it on with relish - it was really thrilling."

Heller spent eight years in Southampton before leaving to join the Anthony d'Offay Gallery, as the director of exhibitions. "This was considered a surprising move by some at the time as it was really unusual to move from the public to private sector," she says.

"But I felt it was an extraordinary opportunity to work on a much more international scale and to work with some of the people who I believed to be among the greatest living artists on the planet. It was an amazing whirlwind experience."

Heller spent two years at d'Offay before returning to the public sector, curating a number of exhibitions, most notably Spectacular Bodies at the Hayward Gallery in 2000. But she feels the commercial know-how she gained at d'Offay, where she worked with artists such as Bill Viola, Gilbert & George and Christian Boltanski, came in very useful at the SLG.

"I don't think I would have been in the position to do what I've done here in the way that I've done it without that experience," Heller says. "It was about getting to know collectors, and working with very high-profile artists. I suppose I have been more ambitious here as a result of the d'Offay experience."

Like many museum directors, Heller spends a fair bit of time on areas such as fundraising, governance and education, but she says it is working with artists that really motivates her: "The raison d'etre of the gallery is the exhibitions programme and that is why I am here as that is my love - it is contemporary art, working with artists and organising exhibitions."

An expanded SLG will give Heller even more opportunities to do this and help the gallery to continue to carry out its original aim - to bring art to the people of south London.

Margot Heller at a glance

Margot Heller was born in 1964 and educated at Sussex University where she studied art history with French.

Her first gallery role was in 1987 at the Giray, a short-lived commercial space in Camberwell. She then spent a short time at the Tate before becoming the assistant curator at Southampton City Art Gallery in 1989, where she later became the director.

At Southampton she bought works by Michael Craig-Martin, Rachel Whiteread and Helen Chadwick.

Art dealer and collector Anthony d'Offay then appointed Heller as his director of exhibitions. She spent two years in this role, before returning to curating in the public sector.

During this time she organised Spectacular Bodies: The Art and Science of the Body from Leonardo to Now at the Hayward Gallery in 2000.

She joined the South London Gallery in 2001. Heller was a Turner Prize judge in 2006.