In 1965, he joined the Ukrainian National Front, an underground organization working for Ukrainian independence from the Soviet Union. On March 29, 1965, his membership in this organization was discovered, and Lesiv was sentenced to 5 years in prison.
He carried out a hunger strike
On October 3, 1977, Lesiv joined the Ukrainian Helsinki Group.
Religious Life 
Yaroslav Lesiv was active in the Ukrainian Catholic Church. From the late 1980s, Lesiv was working towards the restoration of the Ukrainian Catholic church.
In 1988, Lesiv was ordained as a priest in the Ukrainian Catholic Rite.
In 1989, Lesiv visited Moscow twice - including a hunger strike protesting the illegal status of the Ukrainian Catholic Church.
In the night between October 9 and 10, 1991, Yaroslav Lesiv was killed in an automobile accident. He is buried in Bolekhiv, Ukraine.