Sunline recorded 13 wins from her 25 starts in Group One races (a winning strike-rate of 52%), while Makybe Diva, with whom she is often compared, won seven of her 14 (a winning strike-rate of 50%). Greg Childs, the jockey who rode Sunline in 33 of her races, said she deserved to bracketed with the Diva as the best racemares of the modern era. Makybe Diva was an outstanding stayer and Sunline was a champion middle distance horse.
Sunline led in most of her races, and sometimes settled just behind the leader; she was difficult to pass. Sunline was an inaugural inductee into the New Zealand Racing Hall of Fame, along with Carbine, Gloaming, Kindergarten and Phar Lap.
Sunline was foaled at Pleasanton Stud near Cambridge, New Zealand on 29 September 1995. Her sire was the handy Group Two winning English sire, Desert Sun, a grandson of leading sire Danzig, and her dam was the former capable mare Songline by Western Symphony (USA). Sunline came from the same family as Phar Lap, tracing all the way back to his dam, Entreaty, who was her 8th dam. A big strong plain bay with no white markings, Sunline was leased by her breeders Susan Archer and Michael Martin to Takanini trainer Trevor McKee.
In partnership with Thayne Green and Helen Lusty, McKee raced the filly three times for as many wins as a two-year-old.
After a first-up win at three, in August 1998, McKee took Sunline across the Tasman Sea to Australia for the first of an eventual nine visits. Racing in the second, third, and fourth legs of Sydney's Princess Series, for three-year-old fillies, she "powered through the wet" on her Australian debut in the Furious Stakes, won the Tea Rose Stakes on a dry track two weeks later, and won in the Flight Stakes - her first of 13 Group One wins. Sunline was then spelled, rather than continuing on to the feature races in Melbourne, and never competed with the reigning Horse of the Year, Might And Power.