China led the way with installations for a single country, adding 2.4GW in 2019, but most of the activity was again centred in Europe, with the UK (1.76GW) and Germany (1.11GW) adding the most.
Denmark, Belgium, Taiwan, Portugal and Japan also brought capacity online over the 12-month period.
GWEC said the growth of offshore wind globally is set to continue, with a predicted 50GW of new capacity being added by 2024.
New projects in Portugal and Japan give confidence to the rise of floating wind this decade.
"It is exciting to see floating wind capacity being installed in 2019, as once this technology reaches industrial scale, it will open up whole new markets and opportunities for offshore wind," said GWEC chief executive Ben Backwell.
GWEC also predicted a rise in emerging markets this decade. Offshore wind has to date been centred around the European seas and China.
However, new markets such as the US, Taiwan, Brazil, and Australia are set to play an increasing role in offshore wind.
GWEC identified 21 potential emerging markets, which could add more than 80GW of offshore wind by the end of the decade.
"Offshore wind is a huge opportunity to meet our climate targets, as it can replace expensive imported fuels, provide clean energy solutions to countries that have limited land availability, and supply increasingly competitive zero-carbon energy at a massive scale," Backwell added.
"The economic benefits of offshore wind cannot be overstated, with the potential to generate hundreds of billions of dollars in investments, create tens of thousands of jobs and build a supply chain that can contribute to thriving local economies", he said.
GWEC's full annual Global Wind Report is due to be released on 25 March.