The announcement came following the Massachusetts senator's sweeping victory in nine of the 10 Super Tuesday contests and reflects the campaign's strengthened focus on the 2004 election against President Bush.
Johnson, currently a vice president at the merchant banking and private equity firm Perseus LLC, said he looked forward to working with Kerry.
"I have the greatest respect for John Kerry as a friend and as a national leader, and know that he will make an outstanding president," Johnson said in a statement released by the campaign. "Kerry's swift action in beginning the process to select a running mate indicates what type of president the nation can expect -- decisive, focused and ready to lead."
Johnson has an extensive background in both business and government, having served as chairman and chief executive officer of Fannie Mae, a managing director at Lehman Brothers, and an adviser to Vice President Walter Mondale.