Ryan Watson was taken to Wishaw General following an incident in Wilson Street on 11 August but later died.
Police have appealed to people in the local community for information.
Det Insp Mark Bell from Police Scotland said: "From the enquiries my team have conducted so far, I am confident that the answer to Ryan's death lies within the local community of Larkhall."
He added: "A young man's life has been taken away needlessly and the family of Ryan deserve to know the truth about what happened to him.
"Ryan had a partner and a young son who will have to continue their lives without him. His mum and dad have lost a son, his brothers and sister have lost a much loved brother.
"I'm making a direct appeal to those within the community, to search their conscience, and contact us with any information they may have because I know somebody knows who did this."
A murder inquiry has started following the death of a 24-year-old father in South Lanarkshire.