Lynam pleaded not guilty to the charges at the beginning of his trial earlier this month.
However, the jury found he had accidentally poisoned his 21-year-old son, Joel, along with his friends Vincent Summers, 21, and Bryan Wilmot, 30, when he supplied them with the homemade liquor in June 2013.
Lynam was also convicted of a fourth charge of grievous bodily harm after his other son Joshua suffered partial blindness as a result of drinking the concoction.
The Queensland father was charged in late 2013 following Joel’s death in June of that year.
Lynam was unable to revive the 21-year-old after he drank the homemade liquor at the family home at Ballandean, near Stanthorpe, in southern Queensland.
The group consumed the same batch of home-brew during a birthday celebration on the property.
Joel and his friends died of methanol poisoning.
Lynam is expected to be sentenced on Wednesday.