Doyle met his wife Harry when he was volunteering in a soup kitchen. He was nineteen going on twenty at the time, and they seem to have gotten married rather quickly. Doyle was working as a third grade teacher (how he got his teaching credentials so young is beyond me) and was, according to Harry, considerable more "take charge" than he later came to be.
His life changed as he turned 21 and his demon side manifested for the first time. The greenish skin, red eyes and blue spikes that suddenly emerged led to him finally demand some answers from his mother. Doyle couldn't accept his demon side, and this led to great pains in his relationship with Harry, who after the initial shock insisted that they shouldn't let it ruin their marriage. In the end, though, Harry found she was fighting a losing battle, and she left. Her reassurances seem to have been genuine: when she showed up in "The Bachelor Party" she was a demon anthropologist with a demon fiancé. Unfortunately, the demon fiancé turned out to be less than the man of her dreams: when he wanted to ritually eat Doyle's brains before the wedding, Harry broke up with him.
But back to Doyle. After his marriage ended, he turned to drinking, gambling, smoking, and generally turning himself into a miserable slob. At this point, a Brachen part demon called Lucas came to see him, asking for his help against the Scourge, a nazi-like army of demons set on killing all half-breeds. Doyle, eager to save his own skin and not so eager to explore his roots, turned him down. This led to the death of Lucas and his relatives – all of which Doyle got to see in Technicolor with accompanying pain as his first vision kicked in.
What Doyle did after he found he was the new messenger of the Powers that Be isn't known; he certainly seemed well into the role by the time he met Angel, speaking of the Powers as if he knew them well and having learned of the Oracles. Now he was the one to convince Angel to get involved, not just killing evil but actually participating in people's lives. During their first mission they ran into Cordelia, and Doyle found her pretty enough to hire her on the spot. He then spent a lot of his time on the series trying to woo her, in spite of her various rejections. The relationship clearly attempted to be a Katherine Hepburn/Spencer Tracy type of romance; whether it succeeded or not is up to anybody to determine for themselves. (Personally, I think it was the second best modern imitation of the genre, exceeded only by Spike Thomson and Lynda Day in British TV series Press Gang.)
Although Doyle's crush on Cordelia was beyond doubt, it's worth mentioning, if only to please us slashers, that he also admitted to being "a little attracted" to Angel. At the very least, this means that he wasn't the kind of guy to go automatically into homophobic mode. But one of the last things he did was kissing Cordelia, who had finally agreed to dating him. He also transferred his visions to her by that kiss, but whether or not he knew that is hard to tell.
Doyle never gave up his slob lifestyle, and got into money-related troubles with other demons because of it. He often stressed the fact that he wasn't a fighter, almost anxious to appear a coward. In the end, though, that wasn't how he turned out. When the Scourge returned, determined to kill yet another bunch of half-breeds (this time Listers), Doyle was the one to disarm their "Beacon", a device meant to kill anything with human blood within a quarter mile radius. The unplugging succeeded, but Doyle was exposed to the light of the Beacon and burned into nothingness. The episode was aired in November 1999, and presumably the events took place around the same time.
That was the end for Doyle in canon. In fanfiction, it was no such thing.