It's 50 years since Lifeline took its first call - and it's now contacted by more than a million Australians seeking help every year.

The confidential telephone counselling service began in 1963 after a desperate man named Roy called the then-superintendent of Wesley Mission, the late Reverend Alan Walker, on a Sunday night.

Roy told Dr Walker he had just written him a letter which he would receive on Monday morning.

"By that time I will be dead," he said.

"I am sorry to worry you but there is really no one who cares what happens to me."

That phone call and other similar ones prompted Dr Walker to establish Lifeline, which now operates in 19 countries.

Last year, Lifeline counsellors answered 541,450 calls from around Australia, the Wesley Mission said in a statement.

More than a million people nationwide contact Lifeline by phone, email, online or in person each year.

Dr Walker established Lifeline to provide support for the "lonely crowd of the modern city", current Superintendent Rev Dr Keith Garner said.

The Wesley Mission will hold a thanksgiving service to celebrate the milestone in Sydney on Sunday night.

* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14