@IDtoTX, Reliable MArch admission statistics are not readily available, so these are just my observations, based on the experiences of my son and several of his friends and associates.
MArch programs draw heavily from undergraduate BS/BA architecture and architectural studies programs, and increasingly from applicants who have completed the BArch. They all do admit applicants with non-architecture academic backgrounds, but admission is difficult to predict as each MArch program has its own set of admission priorities, with varying emphasis on design, academic scores, diversity factors and life experience. They try to admit a balanced class.
Once admitted, each MArch program also has its own rules determining how long it will take to complete the MArch. Generally, students with an undergraduate degree in architecture will be able to finish the MArch in 2 years while students with other majors may need 3.0 to 3.5 years. But, again, these rules are program specific and vary widely from school to school.
There are about 10-12 very selective MArch programs (I’m estimating under 10% admission rate) MArch programs. The list varies from year to year. The other 30-35 MArch programs including some that are highly rated are overall less selective (in the 40%+ range). All have similar entrance requirements, though these too, are program specific. Generally requirements will include an art/design portfolio (though its weight in admissions varies), a personal statement, recommendations and GRE results. Usually required are courses in art studio and art history and 0 to 2 courses physics and calculus. (You guessed it, these requirements vary too.)
As long as an applicant fulfills the admission requirements, it’s possible to be admitted to any MArch program with an undergraduate degree in anything. If the applicant is aiming for one of the most selective MArch programs, then chances are better with a BS/BA in architecture. Other factors, however, can compensate. These would include an excellent portfolio, work experience in architecture, cultural diversity and unique life experiences.
My son’s undergraduate liberal arts college didn’t offer architecture as a major. He majored in art studio/art history and took a few courses in architectural history and drawing. He attended a summer career-in-architecture exploration program. After graduating he worked for a couple of years in the marketing department of a design focused architecture firm, before applying to MArch programs. Several of his MArch classmates had non-architecture related academic backgrounds – including math, history, sociology and engineering. And several of his successors in his marketing position have also been admitted to top rated MArch programs.
I would say that my son’s exposure to a range of liberal arts disciplines made him a better architect and exposure to the real life practice of architect made him a better MArch student. However, it’s important to note that a 3.0 to 3.5 year MArch is an expensive proposition, so it’s important to look carefully at the financial implications too.