Porter took a secondary job writing for the Indianapolis Journal, recording Indiana Supreme Court decisions, and gained a good reputation with the court. He served as the city attorney from 1851 until 1853, having run for office as a Democrat. In 1853 he was appointed to a vacant reporter seat for the Supreme Court. He was elected to the position in 1854 by a strong majority and served until 1856. That year, he became embroiled in the ongoing political feud between the pro-slavery and anti-slavery factions of the state Democratic party. The pro-slavery faction won, and Porter was among the anti-slavery men expelled from the party, causing him to join the newly formed Republican Party. With his brother-in-law's help, Porter began to organize the Marion County Republican Party, and ran for the city council on the Republican ticket. He served a partial term in the office but resigned in 1859 after having won the 1858 congressional election.