Birchall received a Bachelor of Arts degree from Brigham Young University in 1999.He began working as a financial analyst at Goldman Sachs that same year and left in 2000 to work at Merrill Lynch as a private wealth advisor, where he stayed until 2010. From 2010 to 2016, Birchall was the senior vice president at Morgan Stanley. Since 2016, he has been the managing director of Excession LLC, Elon Musk's family office. He is the CEO of another one of Musk's companies, Neuralink. On a 2018 SEC filing report, Birchall was listed as a director and executive of Musk's tunneling company, The Boring Company.
Neuralink is a neurotechnology company founded in 2016 by Elon Musk and Max Hodak. It is headquartered in San Francisco, California. Birchall is the company's CEO. The company is developing a variety of technologies to treat or cure various neurological diseases and conditions, as well as ones to advance human capabilities to AI levels. One such technology is implantable brain-computer interfaces (BCIs), which allow the human mind and brain to directly communicate with computers. Neuralink is also developing a technology that involves implanting extremely fine wires into the human brain that would connect to a computer. However, some of the claims made in regards to the developing technology's capabilities have been criticized as being an exaggeration by other scientists. Miguel Nicolelis, neuroscientist and head of the Nicolelis Lab at Duke University, called Musk's technology claims "bad science fiction."
Birchall is publicly known for his close, professional relationship with Musk, as director of Musk's family office, the CEO of his company Neuralink, and a director and executive of Musk's company The Boring Company.
In 2019, Birchall testified in a defamation lawsuit trial against Musk, relating to a comment he made about Vernon Unsworth, a British cave diver, in regards to the 2018 Thailand Tham Luang cave rescue of a junior boys' soccer team. Unsworth had said in a CNN interview that Musk's proposed rescue method of a child-sized submarine "had absolutely no chance of working" and that Musk "can stick his submarine where it hurts." Musk made a series of tweets in response, in which he referred to Unsworth as a "pedo guy".
At the trial, it was revealed that under Musk's request, Birchall had spent $50,000 to hire someone whom he believed to be a private investigator, named James Howard-Higgins, to find evidence supporting the claim made against Unsworth. Howard-Higgins was actually a con man and convicted felon. He had emailed Musk after hearing about the Twitter incident and offered his services to look into Unsworth. He made false claims to Birchall that Unsworth had met his wife when she was underage and that he had also been making regular trips to Thailand for decades—a country known for underage sex trafficking and prostitution—in an effort to implicate Unsworth in pedophilic behaviors.
In an email to Birchall sent in August 2018, Howard-Higgins wrote, "Early feedback on the target is there is indeed an unpleasant undertone to some of his lifestyle choices. There is no question that the target 'associates' locally with Europeans who enjoy 'Thai comforts' that are not acceptable in a developed society.” Upon hearing these claims, Birchall told Howard to leak the information to the British media.