In the spring of his senior year, Redskins owner George Preston Marshall offered Baugh $4,000 to play with the franchise. Originally unsure about playing professional football (coach Meyer offered him a job as the freshman coach and he still thought about playing professional baseball), he did not agree to the contract until after the College All-Star Game, where the team beat the Green Bay Packers 6–0.
Baugh was also a baseball player at Texas Christian, where he played third base. It was during his time as a baseball player that he earned the nickname "Slingin' Sammy", which he got from a Texas sportswriter. After college, Sammy signed a contract with the St. Louis Cardinals and was sent to the minor leagues to play with the American Association Columbus Red Birds in Columbus, Ohio after being converted to shortstop. He was then sent to the International League's Rochester, New York Red Wings, St. Louis's other top farm club. While there he received little playing time behind starting shortstop Marty Marion and was unhappy with his prospects. He then turned to professional football.
As expected, Baugh was drafted in the first round (sixth overall) of the 1937 NFL Draft by the Washington Redskins, the same year the team moved from Boston. He signed a one-year contract with the Redskins and received $8,000, making him the highest paid player on the team. He is credited for making the forward pass an integral part of the offensive play in the NFL.
During his rookie season in 1937, Baugh played quarterback, defensive back, and punter, set an NFL record for completions with 91 in 218 attempts and threw for a league-high 1,127 yards. He led the Redskins to the NFL Championship game against the Chicago Bears, where he finished 17 of 33 for 335 yards and his second-half touchdown passes of 55, 78 and 33 yards gave Washington a 28–21 victory. His 335 passing yards remained the most ever in a playoff game by any rookie QB in NFL history until Russell Wilson broke the record in 2012. The Redskins and Bears would meet three times in championship games between 1940 and 1943. In the 1940 Championship game, the Bears recorded the most one-sided victory in NFL history, beating Washington 73–0. After the game, Baugh was asked what would have happened if the Redskins' first scoring drive had resulted in a touchdown. He shrugged and replied "What? The score would have been 73-7."
Baugh's heyday would come during World War II. In 1942, Baugh and the Redskins won the East Conference with a 10–1 record. During the same season the Bears went 11–0 and outscored their opponents 376–84. In the 1942 Championship game, Baugh threw a touchdown pass and kept the Bears in their own territory with some strong punts, including an 85-yard quick kick, and Washington won 14–6.
"I didn't know how much pro players were making, but
I thought they were making pretty good money. So
I asked Mr. Marshall for $8,000, and I finally got
it. Later I felt like a robber when I found out what Cliff Battles and some of those other good players were
making. I'll tell you what the highest-priced boy in
Washington was getting the year before—not half
as much as $8,000! Three of them—Cliff Battles, Turk Edwards and Wayne Millner—got peanuts, and
all of 'em in the Hall of Fame now. If I had known what
they were getting I'd have never asked for $8,000."
Baugh was even more successful in 1943 and led the league in passing, punting (45.9-yard average) and interceptions (11). One of Baugh's more memorable single performances during the season was when he threw four touchdown passes and intercepted four passes in a 42–20 victory over Detroit. The Redskins again made it to the championship game, but lost to the Bears 41–21. During the game, Baugh suffered a concussion while tackling Bears quarterbackSid Luckman and had to leave.
During the 1945 season, Baugh completed 128 of 182 passes for a 70.33 completion percentage, which was an NFL record then and remains the fourth best today (to Ken Anderson, 70.55 in 1982, and Drew Brees, 70.62 in 2009, 71.23 in 2011). He threw 11 touchdown passes and only four interceptions. The Redskins again won the East Conference but lost 15–14 in the 1945 Championship game against the Cleveland Rams. The one-point margin of victory came under scrutiny because of a safety that occurred early in the game. In the first quarter, the Redskins had the ball at their own 5-yard line. Dropping back into the end zone, Baugh threw to an open receiver, but the ball hit the goal post (which at the time was on the goal line instead of at the back of the end zone) and bounced back to the ground in the end zone. Under the rules at the time, this was ruled as a safety and thus gave the Rams a 2–0 lead. It was that safety that proved to be the margin of victory. Owner Marshall was so mad at the outcome that he became a major force in passing the following major rule change after the season: A forward pass that strikes the goal posts is automatically ruled incomplete. This later became known as the "Baugh/Marshall Rule".
"The best, as far as I’m concerned. He could not
only throw the ball, he could play defense, he
could punt the football, he ran it when he had
to. He and I roomed together, and he was a
football man. He knew football, played it, and
everybody had a lot of confidence in him."
One of Baugh's more memorable single performances came on "Sammy Baugh Day" on November 23, 1947. That day, the Washington D.C. Touchdown Club honored him at Griffith Stadium and gave him a station wagon. Against the Chicago Cardinals he passed for 355 yards and six touchdowns. That season, the Redskins finished 4–8, but Baugh had career highs in completions (210), attempts (354), yards (2,938) and touchdown passes (25), leading the league in all four categories.
Baugh played for five more years—leading the league in completion percentage for the sixth and seventh times in 1948 and 1949. He then retired after the 1952 season. In his final game, a 27–21 win over Philadelphia at Griffith Stadium, he played for several minutes before retiring to a prolonged standing ovation from the crowd. Baugh won a record-setting six NFL passing titles and earned first-team All-NFL honors seven times in his career. He completed 1,693 of 2,995 passes for 21,886 yards.
By the time he retired, Baugh set 13 NFL records in three player positions: quarterback, punter, and defensive back. He is considered one of the all-time great football players. He gave birth to the fanaticism of Redskins fans. As Michael Wilbon of The Washington Post says: "He brought not just victories but thrills and ignited Washington with a passion even the worst Redskins periods can barely diminish." He was the first to play the position of quarterback as it is played today, the first to make of the forward pass an effective weapon rather than an "act of desperation".
Two of his records as quarterback still stand: most seasons leading the league in passing (six; tied with Steve Young) and most seasons leading the league with the lowest interception percentage (five). He is also fourth in highest single-season completion percentage (70.33), most seasons leading the league in yards gained (four) and most seasons leading the league in completion percentage (seven).
As a punter, Baugh retired with the NFL record for highest punting average in a career (45.1 yards), and is still second all-time (Shane Lechler 46.5 yards), and has the best (51.4 in 1940) and fourth best (48.7 in 1941) season marks. He led the league in punting from 1940 through 1943. As a defensive back, he was the first player in league history to intercept four passes in a game, and is the only player to lead the league in passing, punting, and interceptions in the same season.
As one of the best-known of the early NFL quarterbacks, Baugh is likely to be compared to more recent great players. When comparing their passing achievements, it should be considered that the football of Baugh's era was rounder at the ends and fatter in the middle than the one used today, making it far more difficult to pass well (or even to create a proper spiral). Additionally, it is important to point out that pass-interference rules have intensified dramatically, inflating modern quarterbacks' statistics.
After retiring from football altogether, Baugh and Edmonia Smith, his wife, moved to the ranch and had four boys and a girl. Edmonia died in 1990, after 52 years of marriage to Baugh, who was her high school sweetheart. According to his son, Baugh derived far more pleasure from ranching than he ever had from football, saying that he enjoyed the game, but if he could live his life over again, he probably wouldn't play sports at all.
Baugh's health began to decline after the death of his wife. During his last years, he lived in a nursing home in a little West Texas town not far from Double Mountain Ranch. The Double Mountain Ranch is now in the hands of Baugh's son David and is still a cow-calf operation, on 20,000 acres (81 km2).
Baugh was the last surviving member of the 17-member charter class of the Pro Football Hall of Fame. Additionally he was honored by the Redskins with the retirement of his jersey number, #33, the only number the team has officially retired.