McCollum announced his plans in a Wednesday telephone call with reporters.
As chief operating officer, McCollum oversees management of power production, transmission, power trading and resource management programs.
McCollum said he plans for the next six months to mainly work on capital project planning.
He said he will have reached five years with TVA in June and that is “an appropriate time” to retire.
A report in November showed McCollum’s compensation totaled almost $2.6 million in fiscal 2011.
TVA is the nation’s largest public utility, with about 9 million consumers in Tennessee, Kentucky, Alabama, Mississippi, Georgia, North Carolina and Virginia.