Wiltshire-based Stand Down aims to provide online counselling to personnel or veterans suffering mental trauma.
It was founded by Kyna Jeng following the death of her 38-year-old brother Anthony, a Royal Engineer, who suffered mental trauma after leaving the Army.
Lynch, from the 90s Irish girl group, took part in a parachute jump over Wiltshire to mark the launch.
A Royal Engineer in the British army for 14 years, Tony Jeng served in Iraq and Afghanistan.
But it was only after he left the Army that his family noticed he was becoming more withdrawn and reclusive.
"He didn't sleep very well, drank a lot more then was healthy and stopped going out of the house," said Ms Jeng.
"Towards the end, he just became a recluse and not participating in life at all."
Despite "reaching out" to the Army and various charities, Ms Jeng said there had been "really no help or support available for him".
"Tony's post-traumatic stress disorder was a significant factor in his early death," she said.
"Unfortunately this situation is not unique, so our main aim is to provide a discreet, easily accessible service to people in my brother's position."
To mark the launch of the independent military charity, Ms Jeng's 17-year-old daughter Paris, along with Lynch, took part in the parachute jump at Netheravon Airfield.
"Keavy is a qualified humanistic counsellor who trained with a friend of mine and she was very, very happy to be the charity's official patron," said Ms Jeng.
"And it was her idea to jump out of an aeroplane from 10,000ft."
A charity offering psychological support to the armed forces has been launched by Keavy Lynch from B*Witched.