Mayer made the announcement to the newsroom Thursday morning, saying it was a tough decision.
"WTVJ has been a part of my life since I began here in June, 1969 as a news intern," he said. "You don’t walk away from a relationship like that easily."
After his stint as an intern, Mayer worked his way from photographer to street reporter to anchor.
Over the years, Mayer served as the station's science and medical reporter, investigative and consumer reporter, crime reporter, business reporter, general assignment reporter and talk show co-host. He's also been anchor of WTVJ's early evening newscasts, weekend newscasts, and midday and morning newscasts.
Since 1990, Mayer has been co-anchoring the NBC morning show, "Today In South Florida." From 5 to 7 a.m., with Pam Giganti. Mayer also served as co-host of "South Florida Today" from 11 a.m.-noon.
Mayer will say his final goodbye in his last on-air broadcast sometime in mid-June.
"It would be impossible to chronicle all that Bob has meant to this station and our people over the years. His intellect, passion and curiosity made him both an extraordinary journalist and an interesting colleague," said WTVJ station manager Ardyth Diercks. "The people of South Florida have been well served by his philanthropy and community service. Our personal lives have been enriched with his counsel, leadership and compassion. And in all ways we are grateful for what he has accomplished and the legacy of integrity he leaves with us."