In the same season she recorded personal bests in the 5000 metres, with 15:57.3 minutes in July in Nairobi, and the half marathon, with 1:09:32 hours in October in San Jose.

[3] She won the 2006 Virginia Beach Rock 'n' Roll Half Marathon,[4] the 2007 Lilac Bloomsday Run and the 2007 Bay to Breakers (San Francisco).

She defeated two marathon debutantes, Shalane Flanagan of the United States and Mary Keitany of Kenya, who took second and third, respectively.

[9] Kiplagat was the race favourite for the 2011 World Championships Marathon and delivered on her form, taking the women's title in a time of 2:28:43 hours.

Her win did not look assured when she fell over in the last 5 km, but her teammate and eventual third placer Sharon Cherop stopped mid-race to help Kiplagat to her feet.

[11] This was her preparation for the 2012 London Marathon, where she was the last runner to challenge eventual winner Mary Keitany and ended the race as runner-up in a personal best of 2:19:50 hours.

Six weeks later she ran at the Great North Run and had a better performance, setting a personal best of 1:07:41 hours while finishing runner-up to Tirunesh Dibaba.

[15] Kiplagat finished runner-up in the London Marathon for the second consecutive year, on this occasion behind Priscah Jeptoo.

[19] 2016 saw Kiplagat return to the Top 3 of major races with significantly faster finishing times than just one year prior.

[21][22] Kiplagat competed in the 2021 Boston Marathon, which had been moved to the Columbus Day holiday in October, less than one month before her 42nd birthday.

She was declared the winner after compatriot Diana Kipyokei, who finished ahead of her by 24 seconds, was disqualified for use of a performance-enhancing corticosteroid.

Her children Wendy and Carlos were at the finish line and award ceremony for her victory in the 121st annual Boston Marathon.