[1] Mason was ranked the number 1 player in the world by Chessmetrics during 11 separate months between August 1877 and June 1878.

[3] Mason made his first mark on the chess scene in 1876 when he won the Fourth American Chess Congress in Philadelphia, the New York Clipper tournament, and defeated Henry Bird in a match by the comfortable margin of 13–6.

At Hastings 1895, often considered the strongest tournament of the nineteenth century,[4][5] he finished tied for 12th–14th with 9½ points of 21 possible.

[7] However, Mason was ranked number 1 in the world, albeit with a slightly lower rating, during 11 separate months between August 1877 and June 1878.

[8] The London System opening 1.d4 d5 2.Bf4 is sometimes called the Mason Variation in his honour;[9] he played it several times from the 1880s.