He briefly coached Finnish club Helsingin Palloseura in 1949 before taking charge at Isthmian League side St Albans City for the 1950–51 season.

[11] He instead began his senior career with Cheshire League side Prescot Cables in late 1932, whilst working as an office clerk.

[15] Soo featured mainly for the Reserves during the 1934–35 campaign, as the forward line of Harry Davies, Joe Johnson, Bobby Liddle, Stanley Matthews and Tommy Sale proved to be highly effective, scoring 60 of the club's 71 league goals on the way to a tenth-place finish.

[16] He broke his leg during 1935–36 pre-season training, but made a speedy recovery to feature in a 2–0 defeat to Liverpool at Anfield on 18 September.

[17] He found himself a first-team regular under new manager Bob McGrory, who utilised him as a left-sided half-back in the place of ageing veteran Harry Sellars.

[18] Stoke were inconsistent across the 1936–37 season, recording a 10–3 victory over West Bromwich Albion (a game which Soo missed due to injury) in the middle of a run of eight defeats in 11 league fixtures.

Soo scored four goals from 45 appearances during the 1937–38 campaign and played at centre-forward on two occasions in November due to injuries to Freddie Steele and James Westland.

[20] Stoke recovered from a poor start to the 1938–39 season to finish in seventh-place, with Soo scoring three goals from 44 appearances, sometimes being asked to play out of position due to injuries to other players.

[23] Soo initially found work in the engineering department of the Michelin tyre company in Stoke-on-Trent, which allowed him to play wartime matches for Stoke City.

[24] Throughout the war he played at full-back, right half-back, left-half-back and inside-left, filling in as need be as team-mates would be unavailable for selection due to service or work commitments.

[24] He also appeared for Newcastle United, Blackburn Rovers, Everton, Chelsea, Reading, Brentford, Port Vale, Crewe Alexandra, Millwall, and Burnley, and played nine times for the England national football team between 1942 and 1945 (in Wartime and Victory Internationals),[25][26][27] the first non-white person ever to play for the national team (albeit in semi-official matches only) and the only person of East Asian descent to date.

[40] However, after going three goals down to league leaders Newcastle United, manager George Martin gave what Soo described as "the most unusual pep talk I have ever heard" and inspired a 4–3 comeback victory.

He then scored five goals in 36 appearances in the 1947–48 season, though new manager Dally Duncan could not take Luton above 13th place, and he allowed Soo to leave Kenilworth Road in the summer.

[51][33] Stan Mortensen wrote in his autobiography, Football Is My Game, that Soo was one of the four best wing-halves he ever played with (alongside George Farrow, Billy Wright and Harry Sellars), and "seemed incapable of a clumsy movement".

[53] Soo spent the summer of 1949 coaching the Finnish club Helsingin Palloseura before entering management full-time at Isthmian League side St Albans City in May 1950.

[55] Padova beat Napoli 2–0 on the final day of the 1950–51 season to avoid relegation out of Serie A, and finished just a point ahead of 19th-placed Roma.

[56] He signed a one-year contract to manage Swedish club Eskilstuna in May 1952, but took charge of the side after first working as head coach of the Norway national football team for the 1952 Summer Olympics in Helsinki.

[61] Soo was appointed manager of newly relegated Division 2 Svealand club Örebro in 1953, however, soon became unpopular with some players in his new dressing room due to his strict training methods.

[62] He was also linked with the Sweden national team job, but the SvFF opted not to appoint a full-time manager following failure to qualify for the 1954 FIFA World Cup.

[63] Back at Djurgården, his physical style of play proved to be highly effective, and he led the "Blåränderna" to the league title at the end of the 1954–55 season, after which he tendered his resignation.

[65] In December 1957, he was appointed as trainer at Allsvenskan club AIK, working alongside former Sweden selection committee chairman Putte Kock.

[65] However, he soon caused controversy after trying to focus his players primarily on football, which angered bandy playing twins Bengt and Björn Anlert.

[69] He subsequently returned to Scandinavia and briefly took charge at IFK Stockholm before he was appointed manager of Norwegian First Division club Fredrikstad in January 1964.

[71] He had a "short and turbulent" reign, again finding his players resentful of his prohibition of alcohol, and led the club to a second-place finish in 1964, before he resigned on 15 December 1964.

[71] In November 1965, he was appointed manager of Danish 1st Division club Akademisk Boldklub, and led the "Akademikerne" to fifth-place and sixth-place finishes in 1965 and 1966.

[73] He remained in Sweden for the rest of the 1960s, though nearly made a return to coaching with the Hong Kong national team in April 1972, though did not take up the post as the HKFA were only prepared to offer him a one-year contract.