Generally speaking, the new rules — six years in the making — require a broader group of professionals to act as “fiduciaries,” the legal term for putting customers’ interests first. They cannot accept compensation or payments that would create a conflict unless they qualify for an exemption that ensures the customer is protected.

If brokers want to receive certain types of compensation that can pose a conflict, they will be required to offer an enforceable contract that promises to put the customer’s interests first.

The firms must also disclose any conflicts and direct consumers to a website that describes how they make money. Firms can charge only “reasonable compensation,” and they cannot offer advisers financial incentives to act in a way that would hurt investors.

In using the contract, brokers will still be permitted to charge commissions and engage in a practice known as revenue sharing, which allows a mutual fund company, for example, to share a slice of its revenue with the brokerage firm selling the fund. Companies that pay more, for example, may secure a spot on the firm’s list of recommended funds.

The rules also aim to protect investors when they roll over money from a 401(k) retirement plan to an I.R.A. Right now, because the recommendation provided is considered “one-time” advice, brokers do not necessarily have to act in the investor’s best interest.

There are piles of money at stake: Individual retirement accounts held $7.3 trillion at the end of 2015, according to the Investment Company Institute, while 401(k)-type plans had $6.7 trillion — money that may eventually be rolled over into I.R.A.s.

Mr. Perez said that government rule makers had made several changes to their last proposal in an effort to respond to criticism and avoid creating a bias toward certain investment products. He said advisers would not be obliged to sell lowest-cost products if a more expensive product like a variable annuity made sense for a particular individual’s situation.