Yokoya Soyo was born in in Genroku 13 (1700), the second son of Yokoya Soju, with an elder brother named Eisei. At the request of others he became the adopted son of Yokoya Somin, and in Kyoho 18 (1733), after Somin's death, he took over the family work at thirty-four and kept the distinguished Yokoya name; in his later years he used the art name Shokei. The published sources describe him as inheriting his father's manner, skilled in both high relief and , and "among the many metalworkers called , an outstanding presence".
His usual work, they write, is on polished , the single-sided chisel line that Somin created. On a polished of bamboo and tiger, his favoured form and method, the commentary praises a chisel that sets bold, powerful beside delicate . On a of lion and peony it notes how he uses chisels of different widths, the strong and fine together, and how the gold inlay on the rim brings colour to a plain surface. A mounting carries his fittings throughout, all on the theme of the gods of good fortune, the , and in .
The other side of his work is high relief with colour inlay on . The published sources say such pieces are few, yet among them they see many fine works with the ability and dignity of Somin's successor. The Yokoya lion, the house subject that began with Somin, appears on a two-piece and . A shows a large kirin rising through auspicious clouds, and his Omori Hikoshichi and Fukurokuju are each called among his finest, the eyes and hands of the figures so alive they seem about to move. A of horses follows Somin's horse faithfully, and another, of eight horses in alone with only the eyes in gold, shows his drawing from life; its rim was later restored by Natsuo.
His fullest work is a matched set of lion-and-peony fittings, , and . It was designated in 1960 and in 1978, and both commentaries stress its rarity: a high-relief is "extremely rare among his works", and the large size and completeness of the set make it probably his masterpiece. Another set carries documents of its own making. On a kirin with matching he wrote his own , which show that the work dates to Horeki 13 (1763), the finished in the tenth month and the in the twelfth.
He signs Soyo with a , cut powerfully in script, the signed on a small tablet. The published sources read him through Somin throughout: the lion, the horse and the all come from the father, while in a crawling-dragon they also find the freshness of added to the traditional house carving.
His record is thirteen designated works, one at and twelve at . One kirin descends from the Tsugaru house of Mutsu. The pieces are the more usual, and a high-relief Soyo set appears only rarely.