The portfolio comprises 19 projects totalling 343MW of generating capacity, with a further 66MW project under construction and due online by the end of February.
The transaction is expected to be completed in the second quarter of 2017. The sell-off will remove all of Infinis's generating portfolio, said Terra Firma, which owns the developer.
It continues to own a portfolio of 14 onshore wind projects currently in the development stage, which Terra Firma said it would "look to sell in due course".
"We are delighted to acquire the onshore operational wind interests of Infinis's UK wind portfolio from Terra Firma. The acquisition continues our investment momentum in renewables, complementing the existing investment base, and increases our renewables energy production capacity to over 3.2GW," said JP Morgan Asset Management chief investment officer of the infrastructure investments group, Matthew LeBlanc.
The deal follows the sale of Infinis's landfill gas assets in December 2016 to 3i Infrastructure.
Terra Firma acquired Infinis in 2003 as part of a larger takeover. Shares in the developer were floated in 2014, but it was taken private by Terra Firma again in 2015 following the UK government's decision to end the exemption of renewable energy sources from the climate change levy (CCL).
Infinis called for a judicial review in to the change in tax exemption, claiming it gave operators far too little warning, but lost the case in the High Court in February 2016 and was dismissed in a Court of Appeal hearing in November 2016.