A native of Chicago, Illinois, McManus spent two years in the United States Army before beginning his professional baseball career in 1920.

He played professional baseball for 22 years from 1920 to 1941, including 15 seasons in Major League Baseball, principally as a second baseman (927 games) and third baseman (725 games) for the St. Louis Browns (1920–1926), Detroit Tigers (1927–1931), Boston Red Sox (1931–1933), and Boston Braves (1934).

In 15 major league seasons, he compiled a .289 batting average (1,926-for-6,660) with 1,008 runs scored, 401 doubles and 88 triples.

McManus also served as a manager or player-manager with several baseball teams, beginning with the Boston Red Sox in 1932 and 1933.

He was also a player-manager of the St. Paul Saints in 1935, the Tulsa Oilers in 1936, the Williamsport Grays in 1938 and 1939, the San Antonio Missions in 1940 and 1941, and the Denver Bears in 1947.

He also served as a manager in the All-American Girls Professional Baseball League for the Kenosha Comets in 1944 and the South Bend Blue Sox in 1945 and 1948.

In 1951, he led an effort to unionize professional baseball, football, and basketball players under the umbrella of the American Federation of Labor.

He compiled a .283 batting average and totaled 31 doubles, 11 triples and 10 home runs in 143 games with the Oilers in 1920.

He compiled a .309 batting average and .367 on-base percentage and finished 15th in the voting for the American League Most Valuable Player award.

He compiled a .284 batting average and .350 on-base percentage and ranked 18th in the balloting for the American League Most Valuable Player award.

He led the league with a 3.76 range factor rating per game at third base and ranked among the league's leaders with 102 runs scored (sixth), nine home runs (ninth), 62 strikeouts (fourth), and 18 double plays turned at third base (third).

On June 30, 1926, with Ty Cobb coaching third base, McManus caught Hall of Famer Harry Heilmann with a hidden ball trick.

[16] On October 2, 1933, the Red Sox gave McManus his unconditional release, and he was replaced as manager by Bucky Harris.

[3] In 1943, McManus was employed as a sheet metal worker doing war work at a Chrysler plant in Chicago.

[28] In April 1944, McManus was hired to manage one of the clubs in the All-American Girls Professional Baseball League.

"[31] He ended up as manager of the South Bend Blue Sox of the All-American Girls Professional Baseball League in 1945.

[33] After compiling a 54–75 record with Denver in 1947, McManus resigned to return to the All-American Girls Professional Baseball League.

[2] In 1948, McManus ended his managerial career with the South Bend Blue Sox, the team he had coached in 1945.

In 1951, McManus led an effort to unionize professional baseball, football, and basketball players under the umbrella of the American Federation of Labor.

[36] McManus died in 1966, shortly after undergoing cancer surgery, at Cochran Veterans Hospital in St.Louis, Missouri.