In a stock exchange notice today (17 November), the trust's board said the motion to amend the investment policy had been approved by 89.6% of shareholders.
Amber Infrastructure Investment Advisor will replace the former investment manager New Energy Solar Manager (NESM).
US Solar fund unveils revised investment policy
Last month, the trust said that as well as changing managers, it would expand its investment mandate, which would come into effect once the appointment was confirmed.
The amendments to the strategy include allowing investment into "development stage assets" and other UK-listed investment trusts, as well as removing the requirement for assets to have additional revenue contracts agreed for a minimum ten-year duration.
Amber, which is a part of Amber Infrastructure Group, is working with NESM to ensure a smooth transition, with a target transition date of 1 December.
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Gill Nott, chair of the trust, said: "Following extensive shareholder consultation, the shareholder vote marked the final stage of a robust and extensive process pursued by the board over the past 12 months to consider all options to protect shareholder value against a challenging backdrop.
"With its 15-year track record in UK investment company management and substantial experience acquiring, developing, managing and divesting utility scale solar projects in the US, the board believes Amber has all the necessary expertise to maximise shareholder value and will put USF on a stronger footing for the future."
Tom O'Shaughnessy, head of North America at Amber, said the firm is looking forward to working with the board, shareholders and the company's advisors.