After his retirement, he coached youth soccer and was a high school physical education teacher at
St. Anthony's High School. Armas served as an assistant coach for the Chicago Fire in 2008 and was the head women's soccer coach at
Adelphi University between 2011 and 2015. On July 6, 2018, Armas was promoted to head coach of
New York Red Bulls after former manager
Jesse Marsch departed the club to join
Red Bull Salzburg as an assistant. Armas helped the Red Bulls finish first in the regular season, winning the Supporters' Shield as a result. The Red Bulls were eliminated in the conference finals by
Atlanta United. In 2019, the Red Bulls finished sixth in the Eastern Conference and were eliminated by the
Philadelphia Union in the first round of the playoffs. The Red Bulls were then eliminated in the group stage of the
MLS is Back Tournament after they were defeated by
FC Cincinnati. The team was in the middle of a scoring slump when Armas parted ways with the club on September 4, 2020, the day after a 1–0 loss to
D.C. United. In 2021, Armas was hired as head coach of
Toronto FC, replacing
Greg Vanney, who departed the club at the end of his contract. On July 4, 2021, following a 7–1 loss to D.C. United, the largest loss in the club's history and a league record of one win, eight losses and two draws, the team announced he had been fired. On December 7, 2021, Armas was hired by
Manchester United as assistant coach to work under interim manager
Ralf Rangnick. He left the club in May 2022. In January 2023, it was confirmed that Armas had re-united with Jesse Marsch at
Leeds United. Armas was named co-interim head coach alongside
Michael Skubala and
Paco Gallardo following the sacking of Jesse Marsch in February, the trio overseeing a 2–2 draw at
Old Trafford with
Manchester United on 8 February 2023 and Skubala acting as solitary interim manager in the home loss against the same opponents four days later. On November 17, 2023, Armas returned to
Major League Soccer, signing as head coach of the
Colorado Rapids. On October 27, 2025, Armas and the Rapids mutually agreed to part ways after missing the MLS Cup Playoffs. On January 7, 2026, Armas was named the head coach of the
Kansas City Current of the
National Women's Soccer League (NWSL). ==Personal life==