WASHINGTON—HSBC Holdings PLC on Tuesday acknowledged that for years it ignored possible money laundering as part of a record $1.9 billion settlement with U.S. authorities that caps the bank's disastrous foray into the U.S. market.

The U.K.-based banking company is expected to forfeit nearly $1.3 billion as part of a deferred prosecution agreement, the largest-ever U.S. forfeiture for a bank, according to people briefed on the agreement between HSBC and multiple U.S. agencies. The deal includes a civil fine of more than $650...