Exhibit 23.1

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM’S CONSENT

We consent to the inclusion in this Registration Statement of ArcLight Clean Transition Corp. II on Form S-1 of our report dated February 4, 2021, which includes an explanatory paragraph as to the Company’s ability to continue as a going concern, with respect to our audit of the financial statements of ArcLight Clean Transition Corp. II as of January 20, 2021 and for the period from January 13, 2021 (inception) through January 20, 2021, which report appears in the Prospectus, which is part of this Registration Statement. We also consent to the reference to our Firm under the heading “Experts” in such Prospectus.

/s/ Marcum LLP

Marcum LLP

Hartford, CT

February 4, 2021