Harris, now vice chairman of wealth management at Morgan Stanley (MS), earned both an undergraduate degree in economics and an MBA from Harvard, before heading to Morgan Stanley. There, she moved up quickly in one division after the next — first, mergers and acquisitions, then equity capital markets, then heading up the bank’s emerging managers platform, where Harris advised women- and minority-owned asset managers.

She has taken a number of companies public, including UPS (UPS) (a $5.5 billion IPO in 1999) and Martha Stewart Living Omnimedia (MSO). Fortune named her one of its 50 Most Powerful Black Executives in America in 2002.

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So what do women entrepreneurs need? A good professional “sponsor,” says Harris, who can provide real access to capital, customers, and industry leaders.

Sponsors, in Harris’s view, aren’t the same as mentors. Sponsors don’t just give advice and offer a sounding board for ideas and worries, they’re active ambassadors for your career or enterprise. A sponsor, says Harris, is someone who will champion you to others (even when you’re not just outside the door). They’re people who will “spend their valuable political capital on you,” she tells Fortune in a recent interview.

For women entrepreneurs, the right sponsor can introduce you to potential customers or gin up additional capital from investors. But for a sponsor to be truly effective, he or she has to understand your business and operations well. That will give them the credibility they’ll need to make a case on your behalf.

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Finally, Harris says a good sponsor “is someone who has the juice to get it done for you.” And by “juice,” she means influence. And then some.

The need for that juice is apparent from the numbers. Women own 30% of U.S. companies — about 7.8 million businesses — but they collect just 11% ($1.2 trillion) of all revenues, according to the most recent annual report from the NWBC, which plays an advisory role to the White House, Congress, and the U.S. Small Business Administration.

Part of the reason, says the council, is that women’s companies aren’t represented as well as men’s in higher-earning industries.

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Harris has shared some of her career-advancement insights (she calls them “pearls”) in a 2009 book, Expect to Win: Proven Strategies for Success from a Wall Street Vet. She has also carved time out for singing performances and to record three albums of gospel music.

There’s little doubt that she feels somewhat evangelical about women entrepreneurs as well. Helping America build and expand more women’s companies, she says, “is a very important mission, especially today.”