In the 2003 NBA Draft Steve was selected with the 28th overall pick by the Washington Wizards. Blake played 75 games his rookie season, averaging 5.9 points, 2.8 assists and 18.6 minutes. He scored in double figures 16 times and tallied a season-high 21 points vs. Miami on March 21, then two days later recorded his first career double-double with 16 points and 10 rebounds against the Utah Jazz. He also dished a season-high eight assists against the New Jersey Nets on January 14, 2004. In his second season, Blake battled through injuries while averaging 4.3 points and 1.5 assists in 44 games for the Wizards.
Steve signed with the Portland Trail Blazers as a restricted free agent in September 2005. He reunited with former Maryland Terrapin and Washington Wizards backcourt teammate Juan Dixon, who also signed with the Trail Blazers in the same off-season. Blake started immediately, playing a significant role when Sebastian Telfair was injured and averaging 26.2 minutes in 68 games (57 starts). He finished third in the NBA in assist-to-turnover ratio and increased his field goal percentage by 11% over the previous season.
In July 2006 Steve was traded to the Milwaukee Bucks. His time with the Bucks was brief, where he averaged 3.6 points and 2.5 assists in 33 games.
Blake was traded to the Denver Nuggets on in January 2007. He averaged 8.3 points, 2.5 rebounds and 6.6 assists in 49 games overall, contributing to a 25-15 record while starting. He scored a career-high 25 points against the Portland Trail Blazers on January 14 and dished out a career-high 18 assists against the Minnesota Timberwolves on February 14. He also started 5 playoff games, averaging 7.2 points, 2.4 rebounds and 4.6 assists in 36 minutes of action.
Steve returned to the Trail Blazers via unrestricted free agency on July 13, 2007. He finished 7th in the NBA in assist-to-turnover ratio during his first season back, posting three double-doubles and scoring a season-high 24 points on January 9 vs. the Golden State Warriors. In his second season back with the Trail Blazers, Steve finished fifth in the NBA in assist-to-turnover ratio. He tied an NBA record most assists in a quarter with 14 in the first quarter against the L.A. Clippers on February 22nd, also a franchise record for assists in a quarter and in a half. He finished that game with season-high 17 assists.
On February 16, 2010 the Nuggets traded Steve to the Los Angeles Clippers where he made 10 starts in 29 games, averaging 6.8 points, 2.4 rebounds, and 6.1 assists. He recorded his first career triple-double with 23 points, 10 rebounds, and 11 assists against the L.A. Lakers on April 14, 2010.
Blake signed a four-year contract with the Los Angeles Lakers on July 8, 2010. He played 79 games in his first year with the Lakers, averaging 4 points, 2 rebounds, and 2.2 assists. In his second Lakers campaign he played 53 games, averaging 5.2 points and 3.3 assists per game. Currently Steve has 2 years remaining on his contract with the Lakers.
On February 19th, 2014, Steve was traded to the Golden State Warriors. Blake averaged 9.5 points and career-highs of 7.6 assists and 3.8 rebounds for the Lakers this season.