Weightman was born on 1 July 1991 in Alnwick, Northumberland, England,[3] where she was educated at The Duchess's Community High School.

Weightman finished sixth in the 1500 metres final at the 2010 IAAF World Junior Championships in Athletics and ended the season with a 1500m best of 4:09.60.

At the 2012 Olympic Games in London, Weightman ran a personal best of 4:02.99 in the 1500 metres semi-finals, and went on to finish ninth in the final.

After running a personal best of 4:20.49 for the mile in 2018, she improved to 4:17.60 in 2019, a time that moved her into the world all-time top 25.

During her career, Weightman was coached by Steve Cram and Mike Bateman (Morpeth Harriers).