Paul McWhir, 51, of Castle Douglas, admitted four charges including rape and acting in a lewd and libidinous manner.
The abuse mainly took place at a farm in Dumfriesshire in the early to mid-1990s.
Sentence was deferred until next month at the High Court in Glasgow.
McWhir preyed on the child for more than three years starting when she was just 10, the court was told.
However, it was only last year that the victim disclosed her ordeal to police.
McWhir was then confronted by his own relatives who demanded he hand himself in.
The court was told the abuse had had a "significant impact" on his victim.
A court has heard how a child abuser was forced to go to police by his own relatives after it emerged he had attacked a young girl.