The
Chicago Cubs selected Stoneman in the 31st round of the
1966 Major League Baseball draft with the 595th overall selection. After signing, Stoneman pitched at three
minor-league classifications in 1966, with
Rookie-level Caldwell,
Single-A Lodi, and
Double-A Dallas-Fort Worth. He started 1967 in Double-A and, after five games pitched, moved to
Triple-A Tacoma. The
Cubs called up Stoneman to the major leagues in mid-season of 1967. He debuted as a
starting pitcher with back-to-back assignments against the
San Francisco Giants on July 16 and 21, allowing three total
runs in 9 innings but gaining no
decisions, although the Cubs won both games.
Manager Leo Durocher then shifted Stoneman to the
bullpen, where he made 26 appearances as a
relief pitcher. He ended his rookie
MLB campaign with a 3.29
earned run average, four
saves and 52
strikeouts in 63
innings pitched. But he was less effective in , with his ERA climbing to 5.52 in only 29 innings of work, and spent part of the season back at Triple-A Tacoma. In the
expansion draft of October 1968, Stoneman was selected by the
Montreal Expos, where he spent five seasons and became a full-time starter for manager
Gene Mauch. He threw his two no-hitters with the Expos: the first against the
Philadelphia Phillies at
Connie Mack Stadium on April 17, 1969. It was Stoneman's fifth major league start and only the ninth game of the franchise's existence; he had eight strikeouts and five walks. The second came at the end of the 1972 season on October 2, when he defeated the
New York Mets in Montreal at
Jarry Park, caught by
Tim McCarver. The latter was the first major league no-hitter in Canada, and both were 7–0 scores. The second included nine strikeouts and seven walks. Stoneman also threw a one-hitter at home in 1971 against the
San Diego Padres, a well-attended 2–0 win on Helmet Night on Wednesday, June 16. In perhaps the best outing of his career, Stoneman struck out 14 and allowed just one base on balls. The only hit came with one out in the seventh inning, a clean single to right field off the bat of
Cito Gaston, which was the Padres' only well-struck ball of the night. He was named to the
National League All-Star Team in
1972 and pitched two innings in relief with two strikeouts. At tall and , Stoneman was a workhorse who over four consecutive seasons (–) logged more than 200
innings pitched. He
struck out 251 in 295 innings in
1971, with a 17–16 record and a 3.15 ERA for non-contending
Montreal(71–90 ()). That season, Stoneman also finished third in strikeouts in the National League, behind
Tom Seaver (289) and
Ferguson Jenkins (263), and his 39 starts tied for the league-high with Jenkins. He also had 20 complete games in 1971, tied for third with
Bob Gibson. His career was shortened by an arm injury in
1973: his
earned run average ballooned from 2.98 in
1972 to 6.80 (
1973), then 6.10 (
1974), for a record of only 5–16 in that span. Overall, Stoneman won 54 games and lost 85 (), with an ERA of 4.08 in 245 appearances. For his career he had 169 starts, 45 complete games, and 934 strikeouts in 1,236 innings. As a batter, Stoneman holds the record with most consecutive games played with at least one strikeout. From April 30, 1971, to April 21, 1972, Stoneman played in 37 consecutive games with at least one strikeout in an at bat. He was left in to bat in the
1972 All-Star Game against
Gaylord Perry, where, he struck out in the bottom of the seventh inning. ==Front office career==