Born in Saint Paul, Minnesota to Mike Floyd Sr. and Theresa Romero, Floyd attended Cretin-Derham Hall High School, where he played for the Raiders football team as a wide receiver. In his junior year, Floyd caught 63 passes for 1,240 yards and 16 touchdowns. As a senior, he recorded 59 receptions for 1,247 yards (21.1 avg.) and 17 touchdowns, and added 497 rushing yards on 43 carries (11.6 avg.) while also returning 16 punts for 373 yards (23.3 avg.) and four more scores, helping lead his high school team to a 13-1 record and an appearance in the state championship game. In order to afford the school, Floyd worked off a scholarship by helping the custodial staff clean the school before the day started. Floyd was named Minnesota Player of the Year twice by the Associated Press (AP) and Gatorade (2007, 2008). He was a USA Today High School All-American in 2007, and was picked to play in the U.S. Army All-American Bowl in San Antonio, Texas.
In addition to football, Floyd also participated in basketball and track while at Cretin. In basketball, he averaged 23.5 points per game as a senior for the Raiders, scoring at least 30 points in six games. He totaled 1,380 points in his basketball career, finishing just 86 points short of the school record for most career points. In track and field, he competed as a sprinter and long jumper during his senior year. He recorded personal-bests of 22.9 seconds in the 200-meter dash and 6.40 meters (20 ft, 6 in) in the long jump.
Considered a five-star recruit by Rivals.com, Floyd was listed as the No. 3 wide receiver in the nation. He was ranked the top wide receiver and the third-best player on the Detroit Free Press Best of the Midwest Top 20 list. Tom Lemming rated him the 15th-best player in the nation, while Scout.com ranked him as the 16th-best. After narrowing his list of college choices to Michigan, Ohio State, Miami, Florida and Notre Dame, Floyd decided to play college football for the Fighting Irish, committing on October 19, 2007.
As a true freshman at Notre Dame, Floyd played in 11 of Notre Dame's 13 games on the year, only missing the final two games of the regular season (Syracuse and USC) due to an injury sustained early against Navy. He recorded seven touchdown receptions on the year, breaking the record for an Irish freshman (previously held by teammate Duval Kamara's four TDs in 2007), while catching 48 balls to break another Notre Dame freshman record in receptions (Kamara had 32 in 2007). His 719 receiving yards set the mark for Notre Dame first-year players (Tony Hunter had 690 in 1979).
Floyd began his sophomore season with 3 touchdowns and 189 yards receiving on 4 receptions. Later in the season, Floyd suffered a fractured clavicle, which prevented him from playing in 5 of Notre Dame's 12 games. He returned from that injury and finished the season with 9 receiving touchdowns and almost 800 receiving yards in 7 games of action.
In 2010, Floyd started every game leading the Irish to an 8–5 record. He ended the season with 79 receptions for 1,025 yards and 12 touchdowns. The 79 catches ranked second in Notre Dame single-season history, while his 12 touchdowns tied for fourth most in a season and his 1,025 receiving yards ranked seventh. Floyd was named MVP for Notre Dame and the Sun Bowl.
After receiving a citation for drunken driving on March 20, 2011, Floyd was suspended indefinitely from the Notre Dame football team on March 21, 2011. The suspension was lifted August 3, 2011, allowing him to return playing football at Notre Dame without missing any games of the 2011 season. Coach Kelly did not however allow Floyd to remain a team captain, leaving senior Harrison Smith the lone captain.
After being suspended from team activities for several months, Floyd was reinstated in August just as fall practice began. In 2011, he started every game leading the Irish to once again, an 8–5 record. He finished the season with 100 receptions for 1,147 yards and 9 touchdowns, including one rushing touchdown. His 100 catches marked a new career best, and also set a new school record, surpassing former teammate Golden Tate's 93 receptions in 2009. He also set school records for career receptions (271), career 100-yd games (16), receiving yards (3,689), and receiving touchdowns (37).
Floyd was taken by the Arizona Cardinals 13th overall in the 2012 NFL Draft.
Floyd began the 2012 NFL season as a backup wide receiver. His first career reception was an eight-yard touchdown off a deflected pass in a 27-6 win against the Philadelphia Eagles. He played in all 16 games with three starts recording 45 receptions for 562 yards and two touchdowns.
In the 2013 season, Floyd started all 16 games recording 65 receptions for 1,041 yards and five touchdowns.
Floyd was released by Cardinals on December 14, 2016 following a DUI arrest.
Floyd was claimed off waivers by the New England Patriots on December 15, 2016. Floyd recorded his first catch as a Patriot in the team's Week 16 blowout win over the New York Jets, a six-yard throw from Patriots backup QB Jimmy Garoppolo. On January 1, 2017, Floyd caught his first touchdown as a Patriot against the Miami Dolphins. He also assisted fellow wide receiver Julian Edelman on his 77-yard touchdown catch and run by delivering a crushing block to Dolphins cornerback Tony Lippett. He was inactive for the final two playoff games as the Patriots advanced to the franchise's ninth Super Bowl appearance. On February 5, 2017, Floyd’s Patriots appeared in Super Bowl LI. The Patriots defeated the Atlanta Falcons by a score of 34–28 in overtime.
On May 10, 2017, Floyd signed with the Minnesota Vikings on a one-year deal worth $1.5 million. After signing with the Vikings, Floyd stated: “I am very excited to come home and play for the Vikings. I have been training extremely hard this offseason in addition to taking responsibility and paying the consequences for my mistake. Although I cannot change my past decisions, I have definitely learned from this experience and look forward to making valuable contributions to the Vikings organization and the Minnesota community, both as a player and a person.” On July 14, 2017, Floyd was suspended for the first four games of the 2017 regular season for violating the NFL Policy and Program for Substances of Abuse.
During his high school years, Floyd was very active in the community, as he was a member of two groups, PRIDE (People Respect-ing Identity Diversity & Equity) and CHOICE (Choosing to Help Others In a Chemically Free Existence). On March 20, 2011, Floyd was arrested for DUI. On December 12, 2016, Floyd was arrested and charged with two counts of driving under the influence after he was found passed out behind the wheel. On February 17, 2017, he was found guilty of extreme DUI, and was sentenced to 24 days in jail and 96 days of house arrest. After his release, he was ordered to pay a fine worth $5115.99 as part of his plea and undergo 30 hours of community service.