Shirl's Speight is the fourth foal out of Perfect Shirl (Perfect Soul), who won the Grade 1 Breeders' Cup Filly & Mare Turf in the US and was also graded stakes-placed in Canada. Her produce includes his full siblings Speightstown Shirl, placed at Grade 3 level in Canada, and Perfect Speighty, a triple winner.

Second dam Lady Shirl (That's A Nice) won the Grade 1 Flower Bowl Handicap and the E. P. Taylor Stakes, then a Grade 2. She has seven winners from ten foals, including Shakespeare (Theatrical), a Grade 1 winner in the US and in Canada, the dual graded stakes winner Lady Shakespeare (Theatrical) and the stakes winner Fantastic Shirl (Fantastic Light).

Third dam Canonization (Native Heritage) was stakes-placed and bred seven winners from seven foals, also including One Wild Woman (Bucksplasher), a stakes winner in the US.

Lady Shakespeare is the dam of Lady Speightspeare, winner of the Grade 1 Natalma Stakes.

Perfect Shirl has a yearling filly by More Than Ready.