Despite the drop, the operator has labelled 2019 a "well-executed year of transition," with April's reduction of maximum stakes on fixed-odds betting terminals from £100 to £2 certainly creating a significant impact for the company.
William Hill was also comparing a 52-week period to a 53-week period for the year prior.
Adjusted operating profit from existing operations fell 37% to £147m, although this was "ahead of management expectations."
This stemmed from exceptional charges and adjustments of £134.1m, primarily in relation to the closure of shops and redundancies.
Overall, William Hill reported a statutory loss before tax of £37.6m, with UK revenue falling 13% to £1.2bn.
However, US net revenue increased 38% to £126.4m, while revenue from the rest of the world rose 71% to £257.4m.
William Hill CEO Ulrik Bengtsson said: "2019 was a year of transition during which we executed on our ambition to diversify internationally, with the acquisition of Mr Green and the continued strong growth of our US business.
"We move into 2020 in a stronger position. Almost a quarter of revenue is now generated outside the UK compared to 15% in 2018."
The immediate market response to the results has been a 3% fall in share price to around £1.71.
