David Exley hopes to raise £10,000 in sponsorship from his motorcycle ride between the charity's 201 branches in memory of the 6,000 people a year who take their own lives.
Mr Exley, who visited the charity's base in Mount Pleasant, Bullbrook, on Thursday last week, said: "I have two very specific reasons for being a Samaritans volunteer.
"Twenty-four years ago my younger brother Tim, at the age of 32, took his own life on Christmas Day.
"Four years ago, my only son James tragically ended his own life. He was 34 years old. It feels as though lightning has struck the family twice.
"I cannot help wondering that if either James or Tim had contacted Samaritans they might be alive today.
"I really hope that my challenge will mean that more people will be aware of the support Samaritans offers, that way, some good can come out of what has been a very difficult time for me and my family."
So far Mr Exley, who has volunteered with the charity for three years, has raised more than £6,000. He started in Worthing, where he lives, on July 2 and will be on the road for seven weeks, finishing in Cardiff on August 20.
To sponsor him, see http://uk.virginmoneygiving.com/davidswayround
A live map of his progress is at www.samaritans.org/david
* Contact Bracknell, Wokingham, Ascot and Districts Samaritans via email@example.com or 01344 455556 or 08457 909090 for confidential, 24/7 listening support.