In 1895, the union was at its lowest point, heavily indebted, with only 236 members at the end of the year. The general secretary Arthur Walker having been dismissed for embezzling union funds, Sims was elected as general secretary and took up the post in March 1896.[2]
Sims prioritised organisation, and quickly embarked on a sixty-day tour of the UK to strengthen existing branches and form new ones. Results were mixed; although he visited several cities where there was no interest, new branches were founded in Norwich, Bradford, Liverpool and Birmingham, and he impressed existing members. He pressed branches to join local trades councils in order to help secure deals with local authorities.[3]
In 1899, ETU members in Bolton walked out. Sims went to the town to try to resolve the dispute; unable to do so, he made the strike official and achieved victory. The following year, he worked with Councillor Richardson to secure a deal with Sheffield City Council; as a result, a large ETU branch developed in the city.[4] That year, he also attended the founding conference of the Labour Representation Committee, although the ETU did not sign up until 1903.[5]
Later in 1900, complaints mounted about Sims' performance; his duties had been neglected, and financial records did not add up. When challenged by the union's executive, he did not offer an explanation, but gave two months notice of his intention to resign.[4]
The executive arranged an audit, which revealed that Sims had embezzled more than £100 of union money; he eventually admitted this, offering as an explanation only that his salary was insufficient. He was charged with theft and sentence to six months imprisonment.[4]