Under the public-private partnership, or P3, the private sector partner is expected to invest between $500 million and $900 million of the total $2.2 billion cost, according to the Maryland Transit Administration.
The private partner will also be responsible for long-term operations and maintenance.
Robert Smith, administrator of the MTA, said he was "quite pleased" with the selections.
"The interest expressed by so many well-regarded companies is a testament to both the value of the Purple Line as a transportation asset and the power of public-private partnership to deliver value for citizens over a long period," he said in a statement.
The state will select a private sector partner late this year or early next year, and construction could begin as early as spring 2015, the MTA said.