Karma, which was formed three years ago and currently employs 251 people, is a new entry at number 22 in the annual 100 Best Companies to Work For list for large firms.
The list is based on surveys of employees and Karma was eighth in the 'my team' category, 18th for 'wellbeing', and 24th in the 'my manager' category. Six in 10 staff earn more than £30,000, the average age is 30 and the male:female ratio is 61:39.
Edelman moved up 50 places to 46th on the 2015 list, which applies to companies with between 250 and 3,500 employees.
The American-owned firm, which employs 424 people in its London operation, was 12th for 'personal growth', 28th for 'my manager' and 41st for 'my team'.
The survey found that staff are excited about where the organisation is going (a 79 per cent positive score) and consider work an important part of their lives (84 per cent, a top 20 score). Two thirds of Edelman’s UK employees are happy with their pay and benefits, and 79 per cent believe the company has a strong social conscience.
MHP owner Engine, with 785 UK employees, moved up one place to 52. It was 27th in the 'my team' category, 50th for 'my manager' and 51st for 'personal growth'.
Work is an important part of life for 84 per cent of staff, putting Engine in the top 15 in this category. Staff overwhelmingly say they can make a valuable contribution (84 per cent) and care about the success of Engine (87 per cent), which spent almost £500,000 on employee development last year.
Weber Shandwick slipped from 70 to 91 on the 2015 list. It was ranked 14th for working in an environment that embraces new technology (83 per cent), while 81 per cent feel the job is good for their personal growth.
More than half the workforce earns £35,000 and above per year and 62 per cent are happy with the pay and benefits they receive. The firm has 294 UK employees.
Other media and advertising companies in the list include PHD Media (16), Abbott Mead Vickers (a new entry at 32), MEC UK (45), Bartle Bogle Hegarty (55), Carat (65) and MediaCom (new at 84).
Online insurance firm Simply Business topped the list, which was published on Sunday (1 March).