The Nielsen ratings company said Monday that 5.9 million people watched Sunday's episode, which featured a gripping confrontation between star Bryan Cranston's Walter White character and the brother-in-law who had suddenly realized White was the drug kingpin he had been searching for.
The Emmy Award-winning series, which began in 2008 on AMC, ends in September.
The largest previous audience for a "Breaking Bad" episode was just under 3 million last August.
"Breaking Bad" has grown steadily through the help of word of mouth and critical acclaim. It averaged 1.2 million viewers per episode for its first season and nearly 2.6 million for its most recent season.
Sunday's ratings also are dramatic evidence of how a critically acclaimed show grows its fan base during a hiatus through people who check it out on DVDs or video on demand.
AMC's new series "Low Winter Sun," with the help of a strong lead-in from "Breaking Bad," was seen by 2.5 million people for its debut Sunday.