Lamb had served as C-SPAN's CEO since he founded the company in 1978 and has been chairman since 1985. Going forward he will be executive chairman of the C-SPAN board.
Even after Lamb formally steps down, he will still host his weekly "Q&A" program on Sunday night.
Sen. John McCain (R-Ariz.) praised Lamb as someone who made "a lasting contribution to our democracy."
"Brian Lamb is a broadcasting legend who made the workings of our government accessible and transparent to every American through C-SPAN, the nonprofit cable network he founded 33 years ago," McCain said Monday, in a statement. "I have had the privilege of knowing Brian for many years, and there are many people across the country who still believe we were separated at birth!
"More seriously, Brian’s unquestioned integrity and profound commitment to making government accountable to the people have made a lasting contribution to our democracy. The American people owe Brian Lamb a debt of gratitude and we wish him all the best in this new chapter of his remarkable career."
This story was updated at 4:06 p.m.