A merger could help the two companies confront declining cigarette sales and diversify in a consumer market shifting toward newer e-cigarettes and other non-traditional products.
The combined company would create a $200 billion cigarette, alcohol, vaping and cannabis giant, and would reconnect the companies: Altria spun off Philip Morris International in 2008, and still owns Philip Morris USA.
The shared history has left the two companies with similar product lines - including Marlboro brand cigarettes - and similar challenges.
Philip Morris said the talks on an all-stock merger of equals were at early stages so there can be "no assurance" that any agreement or final transaction would occur.
Virginia-based Altria posted net earnings of nearly $7 billion in 2018, while Philip Morris took in $7.9 billion.
Altria has diversified beyond the traditional tobacco market, taking stakes in wine, beer and cannabinoid companies as well as the well-known e-cigarette company Juul.