Barbara Mikulski, the longest serving female senator in history, to retire

Sen. Barbara Mikulski, the longest serving female senator in history, will retire at the end of her term, CNN has learned.

The Democrat will make the announcement Monday morning in her hometown of Baltimore.

Mikulski is known as the "Dean" of the Senate women -- helping forge bipartisan relationships for decades that often result in compromise.

Until Democrats lost control of the Senate, she was the chairman of the powerful Senate Appropriations Committee.