Harriet was intelligent, well-read, and charming, though obviously very young, and for a time she involved herself wholeheartedly in her husband's various literary and political projects. But Eliza's residence with them within months of their elopement caused continual friction, and by the fall of 1813 Shelley was gone from home for long periods. Still, in March 1814 the two were remarried in a London church so as to legitimate their union according to English law and provide legal protection to their daughter Ianthe, born in June 1813. At this point, although it appears that the couple intended to live in separate circumstances, Harriet again became pregnant (her son Charles was born on 30 November). Thus when Shelley and Mary Godwin were thrown together in May of 1814, he was all but separated emotionally from his wife.
By July, when Shelley and Mary eloped, Harriet's unhappy, though not impossible, situation seemed clear. With her marriage her father had settled £200 a year on her; Shelley gave her a further £100, which was doubled the next January, after the death of his grandfather. So she was comfortably situated as far as her financial situation was concerned. Yet she was clearly unhappy. For a time she returned to her father's house, but found it overly constraining. At some point she took a lover: anecdote has it that he was an office connected with the military establishment in Chelsea. Sometime in the late summer of 1816 Harriet took lodgings nearby, in Hans Place, Knightsbridge, clearly to shield her family from a pregnancy out of wedlock. In late November or early December, having written a despondent farewell addressed to her father, her sister, and her husband, she walked the short distance from her lodgings to Hyde Park and drowned herself in the Serpentine River. At the time of her death she was just twenty-one years old.