A defender and one of MLS's original players, Vanney spent 10 seasons in the league and another three-and-a-half in the French First Division playing for Sporting Club de Bastia between 2002 and 2005.

In 2017, as coach of Toronto FC, Vanney won the domestic treble by winning the MLS Cup, Supporters' Shield and the Canadian Championship.

Vanney played soccer for Marcos de Niza High School in Tempe, Arizona, and led the team to three consecutive state championship titles in 1990, 1991, and 1992.

In the first six months with Bastia, Vanney helped lead the French club to its first appearance in the Coupe de France Final in over 20 years.

Vanney also spent 11 years as a member of the United States national team, debuting December 21, 1996 against Guatemala, and played 36 games and scored one goal (September 2005).

He was originally named as an alternate for the 2002 FIFA World Cup but initially replaced the injured Chris Armas on the roster after the midfielder picked up an ACL injury in a warm-up friendly against Uruguay on May 12, 2002.

[6] Vanney and his staff, with the support of Grande Sports World and Real Salt Lake, established the first MLS Residential Academy in the United States in fewer than 8 months.

As Director of Soccer Operations, Vanney oversaw program and event development at the Grande Sports World facility featuring 8 professional quality fields; state-of-the-art 58,000 sq ft (5,400 m2) performance center with 4 stadium quality locker rooms; 10,000 sq ft (930 m2) weight room, physical therapy and 16 classrooms.

[18] The arrival of Spanish playmaker Victor Vázquez in midfield at the beginning of the 2017 season saw less responsibility placed on the club's star forward Sebastian Giovinco and captain Michael Bradley to create Toronto's goalscoring opportunities, and this in turn freed up the Italian, enabling him to focus more on his attacking game; furthermore, Greg Vanney's switch in tactics from a 4–4–2 diamond to a 3–5–2 formation benefitted Giovinco's and Jozy Altidore's attacking partnership: by playing closer together, and with Vázquez now supporting them as the team's main creator, the attacking duo began to demonstrate a deeper understanding and an increased awareness of each other's movements, which improved their link-up play, and saw an increase in Altidore's goalscoring output throughout the season.

[22] On September 30, 2017, Toronto FC captured the Supporters' Shield with a 4–2 home win over New York Red Bulls, to clinch top of the league with the most points that season.

[28] After narrowly missing the playoffs in 2021, Vanney's Galaxy finished fourth in the Western Conference (ninth overall) in the 2022 season, the highest positions for the club since 2016.

LA beat Nashville 1–0 in the first round, but fell to rivals Los Angeles FC 3–2 in the conference semifinals.

[29] In 2009, Greg Vanney provided color commentary with play-by-play announcer Kevin Calabro for Seattle Sounders FC games on FSN Northwest and KONG-TV and radio.