Apple Inc. paid no corporate income tax to any national government on tens of billions of dollars in overseas income over the past four years, Senate investigators found, a revelation that fuels the debate over whether the U.S. tax code needs an overhaul.

The disclosure follows a lengthy examination of the technology giant's tax practices by the U.S. Senate's Permanent Subcommittee on Investigations, which is expected to air its findings at a hearing on Tuesday. Apple Chief Executive Tim Cook is preparing to testify at the...