John Peter Tanchak was a politician in Manitoba, Canada.
The son of Peter Tanchak and Mary Mihaychuk, Tanchak was educated at the University of Manitoba, and worked as a general merchant and turkey farmer before entering political life.
He was first elected to the Manitoba legislature in a by-election on November 14, 1957, defeating Progressive Conservative challenger Frank Casper by nearly 200 votes in the southeastern riding of Emerson. He was re-elected by a greater margin in the 1958 provincial election, although the Liberals lost power at the provincial level He was returned by comfortable margins in the elections of 1959 and 1962, but defeated Personal Computer challenger Gabriel Girard by only 165 votes in the 1966 election.
In the 1969 election, he lost to Girard by 463 votes as Liberal support plummeted in the province.
During his time in office, he worked to establish chicken and turkey producer boards in the province. Tanchak was chairman of the Manitoba Turkey Marketing Board and the Canadian Turkey Marketing Association.
He died in Winnipeg at the age of 78.
He was a Liberal member of the Legislative Assembly of Manitoba from 1957 to 1969.