[2] After witnessing the 9/11 attacks, Santarsiero quit his law career and became a high school teacher to "give back more to the community.

[2] In 2016, Santarsiero ran for Pennsylvania's open 8th Congressional District, following the retirement of Representative Mike Fitzpatrick.

He faced fellow Democrat Shaughnessy Naughton in the primary election,[7] whom he defeated.

[8] During the primary, Santarsiero was criticized after his campaign sent out mailers which claimed he "wrote PA’s Gun Safety Law.

"[7][9] PolitiFact rated the claim as "False", given that Pennsylvania's standing gun law was passed in 1995, before Santarsiero was elected to the State House in 2008.

The race was labelled as the only competitive one in Pennsylvania,[10] where both Republicans and Democrats were almost equally present within the district.

[16] Following the passage of Act 13 of 2012, Santarsiero was one of six Democratic state representatives who authored the individual bills making up the "Marcellus Compact."

[19] Following the Sandy Hook school shooting in 2013, Santarsiero introduced a bill in the State House which would mandate background checks for all gun sales.

"[21] Santarsiero has previously stated that proponents of the BDS movement are "misinformed" and any comparisons of Israel to apartheid South Africa is "offensive.

[27] In 2022, Santarsiero defended a "Queer Prom" hosted by a LGBTQ organization where he was present as a chaperone.

[25] Santarsiero and his wife, Ronni Fuchs,[28] reside in Lower Makefield Township, Pennsylvania.