Jessie McIntyre is an agent with the CIA.
She will be, at any rate, not too long after we first meet her. Before her new employers offer her a change in careers, she is a former U.S. Army Ranger working for a private corporation named Thompson Security "providing VIP security services". Having left the military with a rank of Major, it is said that the company was intelligently using "her rank purposely wanting to impress [folks with] her military background". Considering her background, experience, and impressive skillset, that is neither surprising nor upsetting.
One important aspect to that training is her holding the highest military marksmanship rating while in the Rangers; that and the fact that out of a long history never went anywhere without her pistol, "not even the gym". As we are shown this has saved her life on more than one occasions and it does so again when we first meet her. In that case she was returning to her hotel room from exercising when she noticed her door open, heard "the soft spit of a suppressed shot", saw her boyfriend, Tom, fall to the floor, and immediately pulled her piece and ends the threat to her with two in the assailant's chest.
Her preparedness and her instinctive response to danger are two vital elements to take from that scenario. So is the fact that seeing her lover dying on the floor, she hurriedly packed her small belongings, took another last look at him, and then left the area. McIntyre would be the first to admit that deep affections for someone was not a common occurrence.
McIntyre is 34 years old at the initial meeting. She stands a tad taller than most women at 5'10" and while she is said to have inherited her mother's blue eyes and brown hair, "the 135 pounds of lean muscle were all hers, earned in the gym every day". "She had left the service eighteen months earlier; ten years had been enough for her once it became obvious there were just some barriers women were never going to overcome. She had applied to "Q" school two consecutive years hoping to be the first woman to join the Special Forces and wear the beret, but the Army had made it clear it wasn't going to happen. No question she had achieved beyond anyone's expectation and was an excellent soldier, but she finally got the message."
Her job at Thompson was a lucrative one and the frequent first class travel a nice perk but she was quickly finding after just over a year her career was largely providing "personal security services for celebrities and the world's super rich [which] rarely required protecting them from anything more dangerous than themselves".
That is why when the Agency came to visit her and offered a new career, she showed little resistance.