The original church was built in the 1100s as a nave with a narrower chancel to the east, a common early form for Swedish parish churches of the period. During the 1300s the interior was reshaped into a single rectangular room. Around 1500 a sacristy was added north of the chancel, and a porch was built on the south side.
In the 1700s the windows were enlarged to let in more light. In 1755 the south porch was demolished and the south doorway bricked up, with the main entrance moved to the west gable wall — changes that still define the building's appearance today. The church bell is said to still be rung by hand, a detail worth noting for visitors interested in older traditions, though this practice's current status is not confirmed here.
Inside, a stained-glass window depicts the Resurrection of Christ. The chancel holds two medieval iron chandeliers, while the nave has three brass chandeliers. The pulpit was donated to the church in 1755. Among the more unusual furnishings are two funerary hatchments, one for the Lilliehöök af Fårdala family and one for Major Carl Sabelsköld, who together with his wife Ingeborg Rosenstråle donated two decorated candlesticks bearing their coats of arms that remain in the church.
The organ is among the older instruments in the diocese of Strängnäs. It was originally built in 1859 by the organ builder Per Larsson Åkerman for the grammar school in Strängnäs, before being installed in Blacksta kyrka in 1892 with a new façade. It has five stops.