Walter Henry Porter (June 1858 – December 30, 1906) was an American Major League Baseball player born in Vergennes, Vermont who pitched for three teams during his six-year career.
Porter began his career in the short-lived Union Association for the replacement team Milwaukee Brewers. It was for this team that he struck out 18 batters in one game on October 3, . The 18 strikeouts in one game by a losing pitcher stood as the record until Steve Carlton surpassed it when he struck out 19 in one game in . When the Association folded following the season, he was picked up by the Brooklyn Grays, with whom he was their star pitcher. In , he had a record of 33 wins and 21 losses, followed up the next year with 27 wins and 19 losses.
After having a 15–24 record in , Porter was purchased by the Kansas City Cowboys for . He had a record of 18–37, leading the league in hits allowed, runs allowed, home runs allowed, and losses, but on June 6, he pitched a no-hitter against the Baltimore Orioles.
Porter died in Brockton, Massachusetts at the age of 48, and is interred at Calvary Cemetery, also in Brockton.