Ranjitsingh played four years of college soccer at Mercer University between 2011 and 2014. During his Freshman year he was named the starting goalkeeper and made the Atlantic Sun Conference All-Freshman team. By the end of his senior year, he had become one of the top college goalkeepers in the nation, ranking 3rd nationally in total saves and 9th in save percentage. He also earned the Southern Conference's goalkeeper of the year award and was named to the All-Conference team. During his time at Mercer he played 81 matches with 363 saves and 27 clean sheets. He is Mercer's career leader in both GAA and clean sheets. During the summer of 2014, Ranjitsingh played with Sigma FC of League1 Ontario.
On 26 March 2015, Ranjitsingh signed with United Soccer League club Louisville City FC and he made his debut on 20 May in the Lamar Hunt U.S. Open Cup against Lansing United. He served the season as the backup to first-choice keeper, Scotty Goodwin, and played in only one regular season match; a 2–0 loss to the Charleston Battery. At the beginning of the 2016 season, Ranjitsingh was again the backup to Scott Goodwin. On 27 April, he entered the match against the Pittsburgh Riverhounds in the 75th minute after Goodwin was sent off. He started all matches while Goodwin was suspended and was named the primary goalkeeper when Goodwin announced that he was to retire to attend Harvard Medical School. Ranjitsingh would play in 24 of Louisville's 30 regular season matches with 11 clean sheets, including his first 5 starts. He was also the starting goalkeeper for all three of Louisville's USL Cup playoff matches with two clean sheets. During the Eastern Conference Finals match against New York Red Bulls II, Ranjitsingh was injured in the 51st minute while Louisville lead 1–0. He was replaced by Tim Dobrowolski, and New York ultimately won the match in penalties. Ranjitsingh renewed his contract with Louisville City FC and remained their first-choice keeper for the 2017 season. He made his season debut on 25 March against Saint Louis FC, but had to be replaced just before halftime as he suffered a hip flexor injury. He'd go on to miss several weeks and would not return until Louisville's June 3 match against the Charleston Battery where he conceded 4 goals. He would go on to play in 25 of Louisville's 32 regular season matches achieving 11 clean sheets. He played in all four of Louisville's USL Cup matches with three clean sheets. Louisville City would again play the New York Red Bulls II in the Eastern Conference Finals. Louisville would win the match in penalties with Ranjitsingh saving two penalties in the shootout. He also won the award for Fans' Choice Save of the Playoffs for his extra-time save against New York Red Bulls II in the Eastern Conference Final of the 2017 USL Cup Playoffs. Ranjitsingh and Louisville would go on to win the USL Cup Final against Swope Park. in 2018 Ranjitsingh continued as Louisville's starting goalkeeper into 2018 and he made his season debut on March 17 with a clean sheet against USL expansion side Nashville SC. He appeared in 32 of Louisville's 34 league matches with 11 clean sheets. Only missing matches due to a rib injury he sustained on September 22 against Ottawa. He also appeared in all four of Louisville's USL Cup playoff matches; earning a clean sheet in two. Ranjitsingh and Louisville went on to win the USL Cup Final for the second consecutive season. This time against Phoenix.
On 18 December 2018, Ranjitsingh announced via a farewell social media post that he was to depart Louisville City. The following day the club confirmed he was to be reunited with James O'Connor who had left Louisville to coach Major League Soccer side Orlando City earlier in the year. He made his debut for the club on 15 May 2019 in a 2–1 defeat to Seattle Sounders. On November 21, 2019, after O'Connor was sacked, Ranjitsingh had his contract option for the 2020 season declined by Orlando as part of the end-of-season roster decisions.
Minnesota United
On November 25, 2019, Minnesota United confirmed that they had selected Greg Ranjitsingh with the 16th pick in the 2019 End-Of-Year Waiver Draft.
International
Born to a Trinidadian father and Guyanese-Portuguese mother, Ranjitsingh declared his interest in representing Trinidad and Tobago nationally due to his upbringing. In August 2016, Ranjitsingh received a call-up to the Trinidad and Tobago national team for 2018 World Cup qualification. He became the first Louisville City player to be called up for a senior national team, but was an unused substitute in a 2–2 draw with Guatemala and a 4–0 defeat to the USA. On May 20, 2019, Ranjitsingh was added to Trinidad and Tobago's preliminary 2019 Gold Cup roster. He was named to the final squad on June 5. Ranjitsingh made debut for Trinidad and Tobago in a behind-closed-doors friendly on 10 June 2019, playing the second half of a 2–0 loss to Canada.
