Mohamed Taki Abdoulkarim,
who had briefly serving as acting President in 1995, in winning the most votes in the first round, he eventually became President in the aftermath of a series of coup attempts.
Ⓐ who had briefly serving as acting President in 1995, in winning the most votes in the first round, he eventually became( incomplete phrase ..)
Ⓑ having had served as acting President in 1995, in winning the most votes in the first round to became( incomplete phrase ..)
Ⓒ who, having briefly served as acting President in 1995, he won the most votes in the first round in becoming (incomplete phrase ..)
Ⓓ who having had served as acting President in 1995 and winning the most votes in the first round, became (two parts with and are not parallel)
Ⓔ who had briefly served as acting President in 1995, won the most votes in the first round to eventually become (had is used correctly to emphasize that mohammed had served as president in 1995 and now won the election with the majority of votes)