In 1989, Holman was included in a trade on May 25 to the Seattle Mariners along with Randy Johnson and Gene Harris for Mark Langston and a player to be named later (Mike Campbell).

[5] Eleven days later on April 20, at Oakland, he retired the first 26 batters he faced; Ken Phelps' home run over the head of Henry Cotto in right field and turned his near-perfect game into the fourth one-hitter in Mariners history.

[6][7][8] During the late 1980s and early 1990s, Holman logged 32 wins and fourteen complete games, five of those shutouts in two and a half seasons of work.

Holman focuses a majority of his time conducting private and group pitching lessons for both amateur and professional players.

In 2007, Holman was inducted into the "Kansas Baseball Hall of Fame" along with Joe Carter, Bill James and Phil Stephenson.