In 1925, his second season with Philadelphia, Simmons led the AL with 253 hits with a .387 batting average, 24 home runs and 129 runs batted in (RBI). He scored 122 runs, hit 43 doubles, and finished with a .599 slugging percentage. His 85 multi-hit games constitute a single-season MLB record. He earned the second-most votes for the league’s Most Valuable Player Award. In the following three seasons, he hit .341, .392 and .351 and drove in 110, 108 and 107 runs in those respective years, while finishing fifth in 1926 MVP voting and fourth in 1927.

Simmons led the A’s to the AL pennant in 1929 as Philadelphia went 104–46, finishing 18 games ahead of the New York Yankees. The A’s went on to defeat the Chicago Cubs in five games to win the World Series. That season he hit .365 with 34 home runs and led the AL with 157 RBI. He also scored 114 runs, had 212 hits with 41 doubles and a .642 slugging percentage. In his first World Series Simmons batted .300 with 2 home runs, 5 RBIs and scored 6 runs.

Simmons’ best year as a player was in 1930, when he won his first of successive batting titles, hitting .381 with 36 home runs, 211 hits, 41 doubles and 16 triples. He had a slugging percentage of .708, drove in 165 runs and scored 152 runs in 138 games. The A’s won the AL pennant again, going 102–52, and defeated the St. Louis Cardinals to win back-to-back World Series titles. In that World Series, Simmons batted .364 with 2 home runs, 4 RBI with a .727 slugging percentage.

In 1931, the A’s won their third straight AL pennant, by 13.5 games over the Yankees, going 107–45. Simmons won his second batting title, hitting .390 with 22 home runs, 128 RBI, 100 runs scored, 200 hits, 37 doubles, 13 triples and a .641 slugging percentage while playing in only 128 games. He finished third in AL MVP voting behind his MVP teammate Lefty Grove and the Yankees’ Lou Gehrig. The A’s were upset in their quest for a third consecutive World Series title, losing the World Series in seven games to the Cardinals. Simmons hit .333 with 2 home runs and 8 RBI in the series.

In a final season with Philadelphia, Simmons led the AL with 216 hits. He batted .322, with 35 home runs, 151 RBIs and 144 runs scored in 1932. Simmons finished his Philadelphia Athletics tenure with a .356 batting average, 209 home runs, 1,179 RBI and 969 runs scored in 1,290 games. He drove in 100+ runs in all nine seasons and scored 100 or more runs in five seasons. In three World Series appearances for the A’s, Simmons hit .333 with 6 home runs, 17 RBI and 15 runs scored in 18 games.

During his first season in Chicago, Simmons batted .331 with 14 home runs, 119 RBI and 200 hits. In 1934 he batted .344 with 18 home runs, 104 RBI, 102 runs scored and 192 hits in 138 games. After a disappointing final season with the White Sox which saw Simmons bat just. 267 with 16 home runs and 79 RBI in 128 games (first time in his 11-year career he did not reach .300 and 100+ RBI) he rebounded by hitting .327 with 13 home runs, 112 RBI and 96 runs scored in 1936 for the Detroit Tigers.

In 1937 he struggled again, this time with the Washington Senators, batting just .279 with 8 home runs and 84 RBIs in 103 games. He rebounded with a stellar season in 1938, batting .302 with 21 home runs and 95 RBI in just 125 games for Washington. His 21 home runs that year gave Simmons the distinction of being the first player to hit 20 home runs in a year for the Senators.

Simmons was purchased from the Senators by the Boston Bees in 1939. The purchase price was not immediately revealed, though Simmons was reported as not getting along with Senators owner Clark Griffith. Simmons played in the major leagues until 1944.

Simmons was elected to the Wisconsin Athletic Hall of Fame in 1951, the National Baseball Hall of Fame in 1953, and the National Polish-American Sports Hall of Fame in 1975. In a 1976 Esquire article, sportswriter Harry Stein published an “All Time All-Star Argument Starter”, consisting of five ethnic baseball teams. Simmons was the right fielder on Stein’s Polish team. In 1999, Simmons ranked number 43 on Sporting News’ list of the 100 Greatest Baseball Players, and was a nominee for the Major League Baseball All-Century Team. In the 2001 book The New Bill James Historical Baseball Abstract, Bill James ranked Simmons as the 71st greatest baseball player of all time and the seventh greatest MLB left fielder of all time.

Simmons died on May 26, 1956. He had collapsed on a sidewalk near the Milwaukee Athletic Club, where he lived, and was thought to have suffered a heart attack. He was pronounced dead at a hospital a short time later. He was buried at St. Adalbert’s Cemetery in Milwaukee.