MSNBC has not renewed its contract with Joan Walsh, a political analyst who had appeared on the network for years.

Ms. Walsh, who is also a national affairs correspondent for The Nation and was previously the editor in chief of Salon, lamented the decision on Saturday on Twitter, saying she had learned her fate the night before while baking with her daughter.

“I’ve given my heart and soul to the network, from the George W. Bush years through today,” she said. “I’m proud of the work I did.”

Ms. Walsh said in her tweet that she had worked with MSNBC for a dozen years, including six on contract. Network officials could not immediately confirm the length of her time as a paid contributor but issued a statement calling Ms. Walsh “a key voice on MSNBC for years.”