A former coal-miner, Mangnall started his career as an amateur at Maltby New Church, then Maltby Main Colliery, Doncaster Rovers (no first team appearances), then returning to Maltby Main Colliery.

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David Mangnall was turned down by three Football League clubs before gaining a place at Second Division Leeds United in 1927-28. He went un-noticed at Elland Road for two years before winning the managers attention by scoring ten goals in a single Northern Midweek League game. He made his League debut shortly after but nine matches later, one of which was against West Ham United, he was transferred to Huddersfield Town one of the clubs that had originally declined his services. The move enabled him to meet and gain experience from players such as Bob Kelly and Alex Jackson who had helped make Huddersfield Town a dominant force in English soccer throughout the 1920's although the Yorkshire clubs power had begun to wain a little by the time Mangnall joined them.

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His five seasons at Leeds Road seem to have been spent partly on the field but mainly in the treatment room. He did however manage to play in every Huddersfield Town v Hammers fixture during this time and scored for the Yorkshire side in all but one of them.

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In February 1934 David left Huddersfield Town and joined Birmingham, struggling in the lower regions of Division One. The Midlanders avoided the drop that year but were again in trouble the following year when Mangnall was sold to West Ham United West Ham manager Charlie Paynter signed this bustling centre-forward for £2,000 as a replacement for Vic Watson on 14 March 1935. The manager’s faith in the player paid off, as both him and fellow debutant Dr. James Marshall both scored against Port Vale at Vale Park two days later in a 2-2 draw. Mangnall set the Second Division alight in his second season at Upton Park when he scored 22 goals in 25 outings, and numbered two hat-tricks among his harvest of net-finding efforts. After scoring 30 goals in 37 appearances that helped Hammers to within a couple of points of promotion in 1935 and 1936, he was somewhat surprisingly transferred to Millwall the following season, the lad from Wigan Pier territory continued his happy goalscoring trend with the Lions.

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In all bar two of his 67 games for Charlie Hewitts team Mangnall wore the number eight shirt but that didn't prevent him knocking in his quota of goals. Sixteen were struck in 33 League games and a further nine in Millwalls splendid F.A. Cup run which ended at the Semi-Final stage.

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After a few months however Mangnalls relationship with Manager, Hewitt grew strained and came to a head when the player requested a transfer. This was refused and Mangnall was forced to sit out the 1938-39 season without being selected for First team duty. In May of 1939 he was released and allowed to join Queens Park Rangers.

At Loftus Road he played in the three Third Division (South) matches of the aborted 1939-40 season and played regularly for Rangers in the ad hoc Wartime competitions until persuaded to take on the Managers job in 1944. As manager of a Third Division club he added further to his list of achievements . When soccer was eventually restored to its pre-War format he took Rangers to runners-up place in the old Third Division (South) and followed this with the Championship in 1947-48.

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Rangers and Mangnall found the Second Division a bit of a struggle. After a bright start the side eventually finished 13th in 1948-49 but slumped to 20th the following season. They recovered a little in 1950-51 to end in a relatively safe 16th, but plunged to the bottom twelve months later and were returned to the Third Division. Rangers’ misfortunes cost Dave Mangnall his job and he was never involved in football management again.

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The Wigan-born ex-miner later set up in business in Cornwall and accepted an invitation to manage the St. Just Football Club, taking an honorary capacity.