The election agent for Nigel Farage in Clacton Peter Harris said the complaint had been “politically motivated”.
“The facts are clear, the process has been properly followed, and there is no basis for any further allegation, inference, or repetition of these claims,” Mr Harris added.
In a letter, the commission said it had “not identified any omissions of expenditure that ought to have been declared” in Farage’s campaign for his Clacton constituency.
It added: “We did not identify credible evidence of potential offences of electoral law.
“Therefore, our decision is to close our consideration of the matter following initial enquiries and take no further action.”
The claims of wrongdoing against Nigel Farage and his party were made by ex-Reform campaigner Richard Everett.
He alleged the party failed to declare spending on some leaflets, banners, utility bills and the refurbishment of a bar in the Clacton constituency office.
Documents were passed to the Metropolitan Police, which transferred the case to Essex Police.
Earlier this week an Essex Police spokeswoman said: “Any prosecution for such an offence must commence within one year.”
She said an “allegation around misreported expenditure by a political candidate” in July 2024 was made on 5 December.
“It has been concluded that this report falls outside of the stated statutory time limit, and no investigation can take place,” the spokeswoman added.
Farage took over as leader of Reform UK in June 2024, about a month before the general election.
He went on to win the seat of Clacton in Essex from the Conservatives with a majority of more than 8,000.