The Harford confirmed Chubb is making an "unsolicited, non-binding proposal" for the 200-year-old insurance company.
"The Hartford’s Board of Directors is carefully considering the proposal with the assistance of its financial and legal advisors. The Board of Directors is committed to acting in the best interests of shareholders over the long term" the company disclosed in a statement.
Hartford has a market cap of around $23 billion, smaller than Chubb's $75 billion.
Bloomberg News was first to report the possibility of a deal. Other insurers including MetLife and AIG traded higher.