Hired by NBC in 1969, she anchored a half-hour newscast at WRC-TV, its Washington affiliate, in addition to her reporting responsibilities. Mackin received national attention three years later when she became that network's first woman floor reporter at the Democratic and Republican presidential conventions. Her work contributed to the subsequent award of an Emmy to the NBC news team for its coverage. Her report later that year on President Richard Nixon's re-election campaign, in which she stated that the President was saying things about opponent George McGovern that were untrue—the only reporter covering the Nixon campaign to point out Nixon's mendacity—was highlighted in Timothy Crouse's book, "The Boys on the Bus". After a stint in Los Angeles, Mackin returned to Washington in 1974 as the Sunday evening anchor and congressional correspondent.