Mike played baseball and football at Villanova University. He was named to several All-American baseball teams and was drafted by the NY Yankees, Los Angeles Dodgers and the Texas Rangers. In 1972 Siani was drafted by the Oakland Raiders in the first round of the NFL draft and immediately became one of the bright spots on an already powerful Raiders team.
Siani was named to every All-Rookie NFL team and finished second in voting for rookie of the year honors behind Franco Harris in 1972.
Siani played seven seasons for the Raiders, getting to the Pro-Bowl in 1973 and the Super Bowl in 1977 where the Raiders defeated the Minnesota Vikings in Super Bowl XI. Siani was traded to the then Baltimore Colts and after three years in Baltimore, he retired in 1981.