[2] At 16, he moved to Philadelphia to live with and work for Joseph and Collin Cooper, dry goods merchants on Front Street.

[11] In 1832, he bought the resort hotel at Brandywine Springs, six miles west of Wilmington, Delaware, where he owned a vacation cottage; he spent sums to improve the building and its grounds.

[12] In 1839, he retired from the mercantile business and his friend Nicholas Biddle convinced him to become a director of the second United States Bank,[13] where he managed the deposits of Daniel Webster and others.

[15][16][17] Designed by Thomas Ustick Walter, it was built of marble and featured a fresco by Italian artist Nicola Monachesi.

[20] He would spend much of the 1830s on further efforts to raise money for and build a rail line from Philadelphia south to the cities of Wilmington, Delaware, and Baltimore.

Four railroads were ultimately chartered by the various states; Newkirk funded and directed the building of the W&S and the B&PD, then orchestrated its merger with the other two.

In 1838, the merged PW&B began direct rail service between the cities, broken only by a ferry across the Susquehanna River.

Among the railroad's achievements was the first permanent bridge across the Schuylkill River south of Market Street, which the PW&B's directors named for Newkirk.

[28] A deeply religious man, Newkirk served for 34 years as an elder of Philadelphia's Central Presbyterian Church.

[37] In his will, Newkirk bequeathed more than $1 million ($22,900,000 today[21]) to his family, and $500 to the Central Presbyterian Church of Philadelphia to buy books.