Cocaine and heroin with an estimated street value of up to 850 thousand euro was discovered during a raid on a house in Kilcommon on Wednesday.
The planned search was carried out by local Gardaí, backed up by members of the Divisional Drugs Unit, the Dog Squad and detectives from Thurles as part of operation Thor.
A man in his 40s was arrested and is still being held at Thurles Garda Station.
He can be questioned for up to seven days.
Its the biggest seizure in the Tipperary Division this year and one of the largest in recent years.