John B. McDonald (November 7, 1844 – March 17, 1911) was an Irish-born contractor who is best known for overseeing construction of New York City's first subway line from 1900 to 1904.

McDonald won the job with a $35 million bid in 1900, but he did not have the capital necessary to post the surety bonds the city required, so he turned to the banker August Belmont Jr., for financial backing.

The initial segment from City Hall to Grand Central, across 42nd Street to Times Square, and up Broadway to 145th Street—was completed on schedule on October 27, 1904.

In 1905, McDonald was hired away by a rival transit mogul, Thomas Fortune Ryan, who proposed to build a competing subway line.

[6] He also worked on the San Francisco Harbor, the Canadian Pacific Railway, the Entre Ríos Railway in South America, the Northwestern Elevated Railroad in Chicago, a bridge in Montreal and a tunnel in Hamilton, Ontario.