Mr Nyman, who clawed his way back from being 2-0 down in a best of five contest, clinched the title when he won the final game with the word 'wet', netting 20 points.
He said he had been 'living on adrenalin' since the contest began on Friday and had worked hard 'to reach the pinnacle of Scrabble'.
Mr Nyman, 24, said he had learned about 4,000 new words in preparation for the championship which was held in the Plaza Hotel, 'but in the end I only used two of them'. His prize is a cheque for pounds 6,700 and a silver globe.
The final was watched on closed circuit television by an audience of about 200 people. Each new word was recorded on the world's largest Scrabble board measuring 8 sq ft. The most valuable word in the final was 'velures' (another version of velours) which was worth 91 points.
The championship, which has been held once before two years ago in London, was only for the English-speaking world. The 64 entrants from 22 countries could use either English or American versions of words.
Other Britons in the top 20 included: Gareth Williams, 40, a computing lecturer from Cardiff, fourth; Allan Saldanha, the 15-year-old London schoolboy who is UK champion, fifth; Clive Spate, 41, a maths teacher from Mansfield, ninth; Philip Nelkon, 37, a manager of Scrabble clubs, 13th; John Catto, 31, a lorry driver from Dundee, 16th; and Di Dennis, 46, an administration co-ordinator from Wooburn Moor, Buckinghamshire, 19th.