The Prime Minister welcomed the initiative, which she said had taken two years to develop, as she delivered a speech in the northern town on Brexit.
The deal will bring investment and hundreds of new jobs to the area in a major boost for the wind farm sector.
Speaking at the East Coast Hub of offshore wind developer Orsted, Mrs May denied that the announcement had been timed to win over the region’s MPs to support her Brexit deal, ahead of next week crucial meaningful vote.
“This is something that hasn’t just happened this week,” she told reporters.
“It may have culminated this week but I can assure you, it’s been two years in the making - making sure that we get this right. But it’s hugely important for an area like this.
She added: “We are now a world leader in offshore wind and offshore wind is bringing high skilled jobs here and to other parts of the United Kingdom. There are real opportunities.
“What we are aiming for is ensuring that a third of our energy generation is generated by offshore wind by 2030, that is enormous.
“It means significant increases in jobs, in skilled jobs here in the UK. It is good for the UK and it’s good for Grimsby.”