The 23-year-old is highly rated by the national coaching group, but missed out on involvement in the Autumn Nations Series clashes with New Zealand and Argentina after a challenging spell following his return from injury.
Recent weeks have seen Williamson rediscover his form in a Warriors jersey, however, and his performances have been rewarded with inclusion in Gregor Townsend's 40-man Six Nations squad.
Reflecting on the moment he found out, Williamson told Scotland Rugby News: "It was amazing when I found out. John Dalziel - Scotland forwards coach - phoned me last night and I had a good chat with him and it's, yeah, really exciting to get started.
"I called my girlfriend and the parents to let them know because they're always super excited. I'm always the same. It does sound typical but, it is just trying to focus on what I can do better each week.
"Then if I get the selection, it's brilliant and amazing news but if I don't, it means at least I've got something to go back and work on. It's not just, like, sitting thinking about what if and stuff. I need to try and act on what I'm doing."
With Scott Cummings expected to be a key figure in the second row, competition for the remaining lock berth is fierce, with several players in contention.
Williamson is targeting a place in the matchday 23 for the Six Nations opener against Italy and is relishing the challenge ahead.
He added: "Yeah, it's really competitive now for that other spot. I'll be excited to get in there to hopefully try and perform and put myself in the best place to get that opportunity."
Before linking up with the national squad on Sunday, though, Williamson's full attention remains on club duties, as Glasgow Warriors travel to Zebre Parma in the United Rugby Championship on Saturday night.
"You one hundred percent can't overlook Zebre, especially at home," added Williamson.
"They're an excellent side, you know, they've taken some scalps there over the past couple of years so we're fully focused on that and that's the number one job before thinking about anything else properly."