"It feels incredible to finally get out there and get the job done", said Harrison, whose mark moves her to equal third on the world all-time list.
Nigeria, for the umpteenth time, failed to win any shade of medal at the just concluded International Association of Athletics Federations, IAAF World Indoor Championship in Birmingham, England. She has also struggled with illness this week.
"It has been a long time coming but I am finally a senior world champion, so I am so happy", said Johnson-Thompson.
Johnson-Thompson never imposed herself to seriously pull clear until the final event, the 800 metres, which she won easily. I didn't have a place to live properly for a long time.
Leading a United States one-two ahead of IAAF World Indoor Tour victor Christina Manning, world 100m hurdles record-holder Harrison won a golden first major medal, after she missed out on the Rio Olympics and finished fourth at the world championships in London past year. Doubts over her mental strength lingered, so too her ability to compete for the world's top medals when she sometimes struggled in the throwing events.
She famously choked at the World Championships in 2015 when she suffered three failures in her best event the long jump and handed British rival Jess Ennis-Hill the heptathlon title.
Johnson-Thompson had an opening throw of 12.68 metres, 36cm beyond her previous personal best, to keep her in second place after three of the five events.
She will need to be, and a better thrower as well, and this win ought to at least help in the first of those two areas.
She then delivered in the 800m, winning in 2:16.63 to ease out Austria's Ivona Dadic who took bronze with the Cuban clinching silver.
And it gave Johnson-Thompson Britain's first gold at the championships with 4750 points from Dadic with 4700 and Rodriguez with 4637.
Tantalisingly, the difference equated to around a two-second target for Dadic to make up, which is the gap between their two personal bests over that distance indoors.
Could this be a watershed moment in Katarina Johnson-Thompson's career?
In Birmingham, with Olympic and world heptathlon champion Nafi Thiam giving the indoor season a miss and with no javelin - her weakest event - the gold medal was there for her to lose.
"This year it's all about winning medals and titles, something I haven't done for many years, so hopefully this can be the springboard to many more things to come", Johnson-Thompson said.
"At the World Outdoor Championships (last year), I was tenth, and everybody was asking me what went wrong, and people were asking me if what happened last year is going to hurt me".