Born in Dallas, Texas, Hyndman has spent all of his professional playing career in Europe. He joined the Fulham youth academy in 2011 at the age of 15. The midfielder worked his way through the Fulham youth ranks and made his professional debut for the club in the English Championship on August 9, 2014. A couple of years later, Hyndman signed with AFC Bournemouth on a free transfer.
Hyndman joined Rangers in the Scottish Premiership in January of 2017 on loan where he had his most successful professional season, making 13 appearances and scoring four goals. Despite only joining the club in January, Hyndman was selected Rangers Young Player of the Year for the 2016-17 season.
He then went back to the Scottish Premiership and joined Hibernian on loan. He made 19 total appearances for the club, with 15 coming in the Premiership, two in League Cup and two in Europa League Qualifying. Hyndman returned to AFC Bournemouth in January 2019.
Hyndman has represented the United States from the U-17 level all the way up to the senior National Team. He made his USMNT debut at 18 years old when he was subbed on in a friendly against the Czech Republic on Sept. 3, 2014. The following summer, Hyndman captained the United States U-20 National Team in the 2015 FIFA U-20 World Cup, where he played all five matches and scored two goals in group play.