One is the Australian boxer Larry Foley (1847 - 1917). Foley was a successful pugilist who never lost a fight. He retired at 32 and collected a purse of £1,000 for his final fight. So, we can expect that he was known to be happy with his lot in the 1870s - just when the phrase is first cited. The alternative explanation is that it relates to the Cornish and later Australian/New Zealand slang term 'larrikin', meaning a rough type or hooligan, that is, one predisposed to larking about. 'Larrikin' would have been a term that Meredith would have known - the earliest printed reference is also from New Zealand and around the time of the first citation, in H. W. Harper's Letters from New Zealand, 1868:
"We are beset with larrikins, who lurk about in the darkness and deliver every sort of attack on the walls and roof with stones and sticks."