Melanie, 38, said that during her lowest periods she was unable to get out of bed for days.
She was prescribed antidepressants, and she had counselling and alternative therapies to try and rid herself of the illness. But it was only when she found out she and partner Thomas Starr were expecting daughter Scarlet, now three, that her demons left her.
Speaking to The Mirror, Mel said that the Spice Girls success and being thrust into the limelight so rapidly took its toll, leaving her with an unhealthy relationship with food and exercise.
She says she 'became obsessed' about what she ate and cut carbs and protein from her diet, surviving only on fruit and vegetables.
Mel was so desperate to maintain her weight she never ate the food the band's personal chef prepared - but at times she would binge on food. She says she would never purge after eating, and that although she had an 'eating disorder' she was not bulimic. Surviving on a few hours of sleep while on tour, not eating properly and depriving her body of essential nutrients all sent her into an 'awful depression,' she says.
The mum-of-one told the paper that it was on the eve of the Millennium that everything came crashing down around her whilst she was away with her family. She felt so down she was unable to get out of bed. She saw her doctor, who diagnosed her depression - something she found a relief because she knew she could be treated.
Mel says she 'took anti-depressants for 18 months and it was a very gradual road to recovery.'
When she fell pregnant with Scarlet in 2008, she worried the depression might return, but says that being pregnant and having a baby gave her a fresh start and that any 'hangover of a bad relationship with food' disappeared.
"It was the last piece of the jigsaw puzzle," she says.
Did becoming a mum help you focus on the future?