Vélez's career began when the Toronto Blue Jays signed him on August 27, 2001. He had to beg his mother, who wanted him to be an engineer, to sign for him, but she reluctantly did. He began his professional career with the Pulaski Blue Jays in 2003. After three solid years in the minors, he was selected by the San Francisco Giants from the Toronto Blue Jays in the 2005 minor league Rule 5 draft.
San Francisco Giants
In 2006, the Giants assigned Vélez to the A Augusta GreenJackets. He had an exceptional year, winning the South Atlantic League's Most Valuable Player award. He won the award by batting.315 with 63 extra base hits, 64 stolen bases and organization-high 91 runs batted in. The following year, he was placed on the Giants' 40-man roster. He started the year with the AA Connecticut Defenders, but he played so well he earned a promotion to the AAA Fresno Grizzlies. However, he only played four games with Fresno before the Giants called him up for the first time. He made his debut on September 5, as a pinch hitter, as the Giants beat the Colorado Rockies 5-3. He finished the year with four stolen bases, although he only had three hits in 11 at-bats. In 2008, Vélez made the Giants out of spring training, but he was sent down to the Grizzlies in May for Travis Denker. After playing well at Fresno, though, he was recalled on July 8, 2008. On August 30, 2008, he hit his first career home run against the Cincinnati Reds. In 2009, Vélez once again made the Giants out of spring training. He would play in both San Francisco and Fresno during the year, but he spent the majority of time with the Giants. He finished the year with an acceptable.267 batting average. Vélez made the Opening Day roster in 2010. His first appearance of the season came in the Giants' 10-4 victory to complete a three-game sweep of the Houston Astros at Minute Maid Park on April 7. He entered the contest replacing Mark DeRosa in left field as part of a double switch in the seventh inning. The front of his jersey read "SAN." It was the second year in a row that Majestic Athletic, MLB's official uniform supplier, committed a jersey misspelling. Vélez' poor play during the start of the '10 season led to his removal from the Giants active roster when the Giants acquired Pat Burrell. He was called up at times during the later part of the '10 season. On July 26, while sitting in the dugout during a Giants' 10-4 win over the Arizona Diamondbacks, Vélez was struck in the head by a foul ball, coincidentally off the bat of Burrell, and hospitalized briefly afterward. He was placed on the disabled list for a short time after that, but was eventually pronounced fine. However, coincidentally or not, once Velez returned to action in August, he would go hitless for the rest of the season, and then 0-for-37 the following season with the Los Angeles Dodgers
Los Angeles Dodgers
On December 13, 2010 he signed a minor league contract with an invite to spring training with the Los Angeles Dodgers. He joined the AAA Albuquerque Isotopes. He hit.339 in 55 games with the Isotopes and on July 4, 2011 he was called up to the Dodgers. On August 22, Vélez tied J. D. Drew for the worst offensive start for the Dodgers since 1919 by failing to get a hit in his first 25 at-bats. On September 23, he struck out three times to break a 75-year-old record for most at-bats in a season without a hit and tie a 102-year-old record for most consecutive at-bats without a hit spanning more than one season. In the last game of the season, Vélez ground out as a pinch hitter in the eighth inning, finishing the year 0-for-37, the most at-bats in a season without a hit by a position player in Major League history. He also extended his overall hitless streak to 46 at-bats, breaking the record previously shared by Bill Bergen, Dave Campbell and Craig Counsell. On April 8, 2019, Chris Davis of the Baltimore Orioles broke the record when he recorded his 47th consecutive at bat without a hit. On October 4, the Dodgers outrighted Vélez to AAA, removing him from the 40-man roster.
St. Louis Cardinals
On December 21, 2011, Vélez signed a minor league contract with the St. Louis Cardinals.
Toronto Blue Jays
Vélez returned to the Blue Jays organization in December 2012 by signing a minor league contract, with a spring training invitation. He started the 2013 season on the roster of the Triple-A Buffalo Bisons. He was released on July 22.
