What was the major piece of civil rights legislation enacted during the 1960's?
It is hard to say which is more important, the Civil Rights Act of 1964 or the Voting Rights Act of 1965.
The Civil Rights Act made racial discrimination and segregation illegal. It established the rule that essentially all businesses, even though they were privately owned, could not discriminate on the basis of race, religion, and other factors. When it came to employment, they could not discriminate on the basis of sex either.
The Voting Rights Act of 1965 prevented states or localities from having any sorts of voting rules that would "deny or curtail" the rights of minorities to vote. The federal government was given the right to supervise election practices in counties where minority voting had historically been suppressed.
It is hard to say which of these is more important because both the right to be free from discrimination and the right to vote are extremely important rights in a democratic society.