Stephen Miller, Graham Mitchell, Gina Wilson and Frances Ross officially start in their new roles on May 1, in what is one of the biggest senior level moves between Scottish firms in the sector in recent months.
It will take the Simpson & Marwick employment team to nine partners with all four of the new hires based in the Glasgow office but working across the UK.
Mr Miller, who headed the employment practice at MacRoberts, is seen as one of the most prominent employment lawyers in Scotland, with the Legal500 publication describing him as a "very shrewd litigator".
He has been a partner at MacRoberts for 10 years, having previously been with Harper Macleod.
Ms Wilson was appointed as a partner in January last year having spent her entire career with MacRoberts.
Mr Mitchell, who has been a partner for five years, lectures in employment law at Glasgow University, while Ms Ross was a senior associate having spent eight years with MacRoberts.
Sandy Kemp, head of employment law at Simpson & Marwick, said: "With the four new appointments at partner level we believe that we have become unquestionably the strongest employment law team in Scotland, allowing us to advise employers across the country on the most effective ways of resolving issues that arise in the workplace."
Craig Turnbull, MacRoberts managing partner, said the firm was pressing ahead with its expansion plans and a new office in Dundee.
He added: "Three of our partners and one of our senior associates have decided to move on and we wish them the best.
"Partner mobility is now a fact of life for law firms as demonstrated by the fact that MacRoberts attracted three new partners in 2012."
Earlier this month MacRoberts reported a 4% dip in turnover to £17.3 million in 12 months to April 30.