The company said on Wednesday that Rosalind Brewer will join Starbucks as chief operating officer and group president on October 2, becoming the second highest ranking executive at the company after President and CEO Kevin Johnson.

Brewer, who resigned from Wal-Mart Stores (WMT) unit Sam’s Club in January, will be responsible for Starbucks’ operating businesses across Canada, the U.S. and Latin America, as well as the global functions of supply chain, product innovation, and store development organizations. She is the first woman and first African-American to hold such a high position at Starbucks. Brewer was No. 19 on last year’s Fortune Most Powerful Women list.

Starbucks has been striving to quicken service at its stores and more seamlessly integrate its mobile ordering service. As Fortune‘s Beth Kowitt reported in June, Starbucks is looking to expand and iron out the logistics so that the system, aiming to facilitate speed and convenience, doesn’t leave customers frustrated and cooling their heels. Some 25% of orders at Starbucks are placed or paid for via its mobile app.

For her efforts, Brewer, will be well paid: a regulatory filing including her employment contract said she will get an annual base salary of $1 million, as well as a $7 million equity bonus and a $1 million signing bonus.

Brewer was already a Starbucks board member, helping her land the job. “She has been a trusted strategic counselor to me ever since she joined our board of directors, and I deeply value her insight, business acumen, and leadership expertise,” Johnson said in a statement.

She joins Starbucks as the company looks to kickstart U.S. growth. A slowing pace of sales gains in the U.S. forced Starbucks to cut its profit forecast for the fiscal year in July, when it also announced it would shutter its Teavana stores.

While well regarded, Brewer struggled to narrow the chronic sales growth gap with arch-rival Costco Wholesale (COST). On her watch, Sam’s Club made large strides in e-commerce with initiatives such as drive-through pick up of online orders and scan-and-go, which allows members to scan items with their own phones and speed up checkout. The $57 billion a year Sam’s Club chain has also been repositioning itself to attract a more affluent clientele (Brewer ambitiously and perhaps unrealistically wanted to take the average household income of a Sam’s shopper to $100,000 from $80,000), overhauling its grocery offering (60% of sales) and streamlining and improving Sam’s private label brands. But Costco’s more affluent clientele and better locations have proven hard to overcome.

Brewer, who had been Sam’s CEO since 2012, also worked at consumer products maker Kimberly Clark (KMB) for 22 years before that.