Theisen-Eaton, from Humboldt, Sask., gathered 6,808 points to win the prestigious competition for a second time after 2013. Second-place Carolin Schaefer of Germany had 6,547 points and Nadine Broersen of the Netherlands took third with 6,531.
"It's the best feeling in the world. I am just happy," Theisen-Eaton said. "I didn't expect to score this high. It's going to be hard to get a better score again this year. My goal is Rio and the Olympics. I am just going to live in this moment for the next little while."
Olympic champion Jessica Ennis-Hill finished fourth in the Briton's first heptathlon since winning gold at the 2012 London Games. Ennis-Hill earned 6,520 points and comfortably passed the 6,200-point qualifying mark for next year's Rio Olympics.
"I feel so happy. It's an amazing feeling to be back," said Ennis-Hill, who recovered from an Achilles tendon injury and gave birth to her son last year before resuming training in November.
"I was really pleased to score that high but I am disappointed with a few events," she said. "My goal was to get the qualifying for the Olympics. I just proved to myself that I still got it in me, that I still got that competitive edge."
Dafne Schippers was second before the final event and looked set to beat her own Dutch record of 6,545 points but decided not to start in the 800 metres because of a knee injury.
Kazmirek held on to his lead from the opening day of the IAAF World Combined Events Challenge to finish on 8,462 points, just nine short of his personal best. Michael Schrader came 47 points back in second, and Willem Coertzen of South Africa gathered 8,398 to take third.
"This is a huge relief," said Kazmirek, adding he struggled with a groin injury recently. "I couldn't train like I normally do so I am pleasantly surprised."
Damian Warner of London, Ont., the 2013 champion, won three events but was no contender for the overall victory after failing to score points with three invalid attempts at the shot put.
Olympic and world decathlon champion Ashton Eaton pulled out citing lower back problems shortly before the start Saturday.