The Cavaliers began play in the 1970–71 NBA season as an expansion team. They set losing records in each of their first five seasons before winning their first division title in 1976. That team was led by Austin Carr, Bobby "Bingo" Smith, Jim Chones, Dick Snyder, Nate Thurmond, and head coach Bill Fitch, and was remembered most for the "Miracle at Richfield", in which the Cavaliers defeated the Washington Bullets 4–3 in the Eastern Conference Semifinals. They won Game 7, 87–85, on a shot by Snyder with four seconds to go. The Cavaliers moved on to the Eastern Conference Finals for the first time, but were without Chones after he broke his foot in a practice right before the series opener. As a result, the Cavaliers went on to lose 4–2 to the Boston Celtics. They made playoff appearances in the following two seasons before going on a six-year playoff hiatus.
The early 1980s were marked by Ted Stepien's ownership, who had a disastrous run as owner and de facto general manager between 1980 and 1983. During Stepien's reign, the Cavaliers made a practice of trading future draft picks for marginal veteran players. His most notable deal sent a 1982 first-round pick to the Los Angeles Lakers in exchange for Dan Ford and the 22nd overall pick in 1980. As a result of Stepien's dealings, the NBA introduced the "Stepien Rule", which prohibits teams from trading first-round draft picks in successive seasons. The Cavaliers went 66–180, dropped to the bottom of the league in attendance and lost $15 million during Stepien's three years as the owner. The Cavs went through six coaches during that span, including four during the 1981–82 season. The team finished 15–67, and between March and November 1982, the team had a 24-game losing streak, which at the time, was the NBA's longest losing streak. George and Gordon Gund purchased the Cavaliers from Stepien in 1983.
The Cavaliers made the playoffs ten times between 1984–85 and 1997–98. In 1988–89, the Cavaliers had their best season to date, finishing the regular season with 57–25 record behind the likes of Brad Daugherty, Mark Price, Ron Harper and Larry Nance, and head coach Lenny Wilkens. They had their second 57-win season in 1991–92 and reached the Eastern Conference Finals that year. However, between 1998–99 and 2004–05, the Cavaliers failed to make a playoff appearance. The 2002–03 season saw the Cavaliers finish 17–65, tied for the worst record in the NBA.
The Cavaliers' luck changed as they landed the number 1 pick in the 2003 NBA draft. The team selected heralded forward and future NBA MVP LeBron James, a native of nearby Akron who had already risen to national stardom at St. Vincent-St. Mary High School. In 2005, the team would be sold to businessman Dan Gilbert. That year, the team also hired head coach Mike Brown and general manager Danny Ferry. The Cavaliers built a team around James and Žydrūnas Ilgauskas by adding players including Drew Gooden, Larry Hughes, and Anderson Varajao. Under this new leadership, the Cavaliers made five straight playoffs from 2006 to 2010, advancing to at least the second round each time. The 2006–07 Cavaliers advanced to the franchise's first NBA Finals, but were swept by the more experienced San Antonio Spurs. The 2008–09 Cavaliers won a franchise record 66 games, including a franchise-best 39–2 record at home, but lost the Eastern Conference Finals to the Orlando Magic. Despite the addition of four-time NBA champion Shaquille O'Neal, the 2009–10 Cavaliers were unable to return to the Eastern Conference Finals after losing to the Boston Celtics in the second round.
With the Cavaliers out of the playoffs, the focus turned to James' impending free agency. On July 8, 2010, James announced in a nationally televised one-hour special titled The Decision that he would be signing with the Miami Heat. The repercussions of this announcement left many in the city of Cleveland infuriated and feeling betrayed. After a 19–win season in 2010–11 (the 42-win difference being the biggest single-season drop in NBA history), the Cavaliers began a rebuild around Kyrie Irving, who they selected first overall in the 2011 NBA Draft.
In 2014, James returned to the Cavaliers after four seasons in Miami. While the Heat had a 224–88 record during James' four-year tenure and won NBA titles in 2012 and 2013, the Cavaliers went 97–215 and missed the playoffs each season. The Cavaliers made several moves to build a championship-contender around James, most notably acquiring power forward Kevin Love from the Minnesota Timberwolves, which created what many fans and media referred to a "Big Three" with James, Love, and Irving. The Lebron-led Cavaliers made four consecutive finals appearances in from 2015 to 2018, all against the Golden State Warriors, winning in 2016. The 2016 NBA Championship marked the Cavaliers' first title in franchise history, as they became the first team to come back from a 3–1 deficit to win the Finals. It was also Cleveland's first championship in major professional sports since the 1964 Browns, signaling the end of the so-called Cleveland sports curse.
The Cavaliers' roster went through many changes in the 2017–18 season, most notably the trade of Irving to the Boston Celtics in exchange for Isaiah Thomas and other assets. Thomas was later traded to the Los Angeles Lakers as part of a trade deadline overhaul that saw the Cavaliers add several young players. The following offseason, James declined his player option to rejoin the team, instead signing with the Lakers.