The Unite general secretary, Len McCluskey, has been cleared of breaching union rules during his narrow re-election over Gerard Coyne last year.

Coyne submitted a number of complaints accusing McCluskey and his staff of manipulating union procedures to their advantage, but the trade union watchdog has dismissed the claims.

“None of the complaints succeed and they are therefore all dismissed,” the certification officer ruled on Friday. “I have not, therefore, had to consider remedies.” It follows a ruling in May that the vote for the most senior position in the union would not be subject to a rerun.

The assistant general secretary, Gail Cartmail, who was acting general secretary during the election, said the ruling was correct.

“Every charge brought against our union by Gerard Coyne and his campaign has been dismissed and shown to be misconceived, underscoring once again that our election was, as we have always said, conducted freely and fairly,” she said.

“This is an emphatic ruling that ought to draw a line under matters once and for all, allowing this union to do what it does best, defend the interests of its members.”

The battle to be leader of the union, which is Labour’s largest donor, was viewed by many as a proxy war for control over the direction of the party because Unite supports Jeremy Corbyn, while Coyne was seen to be closer to the party’s right wing.

The watchdog criticised aspects of Coyne’s campaign which it found included misleading information in some of the literature.

Unite said Coyne’s campaign produced a publication, Unite Herald, to “misinform and mislead our members” which filed “empty complaints designed to pollute opinion of our union”.

Cartmail said: “This organised effort by external reactionary forces to interfere in Unite’s democracy has predictably failed. Those who have attempted to smear this organisation for their own ends should hang their heads in shame.”

Among his 10 complaints, Coyne said there should never have been an election because there was no genuine vacancy. He argued that McCluskey resigned, prompting the election, in an attempt to give himself an unfair advantage.

Although the certification officer threw out Coyne’s complaints, it said: “The calling of an election a year earlier than anticipated by Gerard Coyne undoubtedly put him at a disadvantage as compared with Len McCluskey, who had a long-established track record in the post and a substantial and developed support network.”

It is understood Coyne will not appeal against the decision. In a statement after the ruling he expressed his disappointment and thanked everyone who had given him their support and voted for him.

McCluskey won the April 2017 election with 45.4% of the vote to Coyne’s 41.5% on a turnout of 12.2%.