Grey designed many noted landmarks in Southern California, including the Beverly Hills Hotel, the Huntington Art Gallery, the Pasadena Playhouse and Wattles Mansion.

He is credited with being one of the pioneers in the development of the new American architecture in the early 20th century, with a focus on harmony with nature and eliminating features not belonging to the local climate and conditions.

[2][3] In 1890, the 18-year-old Grey won first prize in a competition for the design of a water tower and pumping station sponsored by a New York architectural publication.

[3] When Grey went into practice on his own, he first attracted attention for his design of a summer home he built for himself on a bluff overlooking Lake Michigan at Fox Point, Wisconsin.

"[3] From 1907-1908, Hunt & Grey designed a Beaux Arts mansion for railroad and finance magnate, Henry Huntington, in San Marino.

"[5] While a French influence was requested by Mrs. Huntington, Hunt & Grey also added elements of a new California architecture by including a red-tile roof, unornamented plaster walls, and sage green window trim.

Guy Cochran near Downtown Los Angeles that Gustav Stickley's The Craftsman magazine dubbed the "very best" of their work, with enormous windows "looking out upon the terrace and garden, giv[ing] such a sense of relationship between the two that there is almost no feeling of being enclosed within walls.

"[7] The Craftsman referred to Hunt & Grey as "pioneers in the development of the new American architecture," which was "but a series of individual plans adapted to the climatic conditions and to the needs of daily living" and in harmony "with the natural environment and contour of the landscape.

"[9] Though often associated with the Craftsman movement, Grey's structures reflect a wide variety of styles, including Beaux Arts, Mission Revival and English Tudor.

"[1] After his partnership with Hunt dissolved in 1910 or 1911, Grey went on to design the Pasadena Playhouse, the Beverly Hills Hotel, the Lincoln Shrine in Redlands, three buildings for the First Church of Christ Scientist, and many residences.

After completing his first Christian Science church, Grey published an article about church design in which he wrote: "The commercial spirit of our age is so inclined to be a mad race for the 'almighty dollar,' and commercial structures are so often built with the idea of obtaining the most show for the least money that when religious organizations build they should show that their aims are higher.