The Abergavenny-based rider triumphed in the women's 500m time trial, forcing Victoria Williamson into second place with a finish time of 34.763s.
Danielle Khan came in third on 36.04s, while James's sister Rachel finished fifth.
"This is the start of my season now," James told British Cycling. "The beginning of the season hasn't been a very good start with appendicitis and an Achilles injury.
"So this is the beginning of my season and it is really good to go out and set a PB (personal best) when I'm still in a hard block of training."
Doull secured victory in the men's individual pursuit champion, fending off a tough challenge from Jon Dibben in the final.
Meanwhile, Paralympic gold medallist Mark Colbourne took silver in the paracycling time trial.