Sobrato began his own real estate investing in 1957, while still in college at Santa Clara University. Beginning in 1972 he worked closely with another successful Silicon Valley investor, Carl Berg, for many years. He founded the Sobrato Organization in 1979; his son, John Michael Sobrato, took over leadership of the company in 1998. The company grew to hold more than 110 commercial buildings and more than 30 apartment complexes. In 2013, both father and son announced that they were moving away from managing the operations of the company to focus on charitable activities.

Sobrato and his family are listed at #110 on the 2014 Forbes 400 list with an estimated net worth of $4.8 billion, and at #340 on The World’s Billionaires list as of May 10, 2014.

Sobrato and his son have both signed on the Warren Buffett’s Giving Pledge to donate their wealth for charitable purposes. By the close of 2014, the Sobrato Philanthropies (which encompass the Sobrato Family Foundation, family-directed giving, and corporate giving through The Sobrato Organization) had given more than $314 million in money and property. Major beneficiaries have included Santa Clara University, Sobrato High School, and Bellarmine College Preparatory. In 2015, he and his wife offered the biggest ever individual pledge to the University of San Francisco, worth $15 million.